In the week in which the Ordnance Survey triangulation pillar celebrates its 80th birthday comes news that uber bagger Rob Woodall has become the first person to visit every one of them, finishing his round of 6190 British trig points on Benarty Hill in Fife on 16th April. How long did it take him? How hard was it? ...and what was the point?

• ​Rob has major form completing challenging lists, including the first round of all 1556 Marilyns. For our interview on that see here

Congratulations! Did you have company for the last one, and was it a bit of a party?

There were 29 folk on Benarty. It coincided with the Triggers Spring Meet which was at Comrie this year, but quite a few others joined me, including the OS's head of media who flew up from Southampton!

"We've been hugely impressed by Rob's 13-year mission to bag all of Britain's remaining trig pillars, since first hearing about it last year, and inviting Rob to write a guest blog for us" says Andy Steggall, Senior Press Officer at the the OS. "When we realised that Rob would be bagging his final trig pillar at Benarty Hill in Fife, we asked to come along on the day and celebrate with him and presented Rob with a special mounted flush bracket to mark his fantastic achievement. By coincidence, it was just two days before we were celebrating the 80th anniversary of the trig pillar being used to map Britain, so it was an added reason to celebrate! Well done to Rob and we look forward to hearing about any future challenges"

How long have you been at it?

I started taking an interest in 2000, but didn't start making proper logs (including on trigpointing.uk) until Sept 2002, so it took me 13.5 years to finish.

Do you know of anyone else who's working through the trigs?

I keep a league table (the Triggers 1000 Club) which currently lists 47 folk who have more than 1000 extant pillars (i.e. excluding ones they couldn't find or were already destroyed). Neither the 2nd nor the 3rd on the list use TrigpointingUK or any of the other sites, so it's obviously possible that someone else has a large number or even all of them. Hopefully the publicity surrounding my own completion will flush out a few more with big totals.

Does the 6190 figure cover all the UK's trig points, including Northern Ireland?

My total includes several which have been destroyed since I saw them. It includes OSGB i.e. not OSNI or OSI - the two Irish agencies have separate networks, although the dozen or so Primary stations were tied into the main OSGB network - quite a thought when you consider the logistics of making sightings across the Irish Sea. It excludes non-pillar trigs such as roof bolts, blocks, Berntsens and Intersected Stations such as church steeples and lighthouses. Including all types of OSGB trig there are over 25,000 - although many are destroyed or hard to find / access.

How does one come by reliable info on the number and location of all the UK's trig points – did you get a list off the OS?

The lists used by the websites came from the OS, but as far as I know they don't maintain a list nowadays, as most of the trigs have been superceded by GPS. Graeme Paterson keeps track of lost pillars - and occasional refound ones - in the files area at https://groups.yahoo.com/neo/groups/trigonomy/info and this is probably the most authoritative source. In terms of where they are, Trigpointing.uk is a good place to go. Haroldstreet.org.uk is another.

It's a pretty unusual list, to say nothing of the scale of it – so what inspired you to start visiting them systematically?

Dave Hewitt hit on the idea of bagging one of every available height - i.e. Ben Nevis marked on the map as 1345m; Little Ouse at -1m (yes below sea level!) and this seemed a good plan - especially for someone living in hill-starved East Anglia. Another idea of Dave's was to bag all the trigs on Landranger Sheet 119 (the Peak District) - this map has more pillars than any other map, at well over 100. This provided a framework but of course I bagged others en route, and started to wonder whether it might be feasible to bag the full set.

It sounds like there's a huge variety of locations, from remote mountain tops to suburban back yards (!) – how much was this diversity a big part of the appeal, for you?

This is part of the appeal - and yes there are quite a few in people's gardens. An interest in mapping is another. The challenge of a really big list was certainly part of it too.

What was hardest about the whole process? (the travel? The research?...)

Maybe the travel. I didn't do that much research. I'd sometimes encounter a trig I couldn't find or couldn't access, and these needed research. Pre-researching was generally too much effort - I prefer being out bagging.

Can you describe some of the most contrasting trig locations?

They rarely involve scrambling (try it with a heavy theodolite in your backpack) but classic locations such as An Teallach, Liathach and Cul Mor contrast hugely with the much more common agricultuiral trigs such as my nearest, Haddon Lodge just outside Peterborough. However, there are low level trigs which have a charm of their own, especially coastal trigs. I was out at Angle Bridge today, another local pillar, watching a pair of Great Crested Grebes.

Is it true that some trig points are falling into disrepair, or disappearing beneath the undergrowth? Were there any that were especially difficult to find?

Many low level pillars are hard to find. Some of the Cornish ones are legendary - covered in ivy and brambles and impossible to see - hard to find even with a GPS. Previous logs on the Trigpointing website can be invaluable. One in Suffolk was reported missing - I couldn't resist returning with my secateurs and thornproof jacket to prove the reports wrong !

And which are technically or logistically the hardest to get?

Some of the MOD sites can be difficult. Eastriggs near Dumfries took a few emails and phone calls to arrange. The Palmerston Forts (Napoleonic era defences) often have trig pillars, and one in Kent which is now used as a smallholding took a couple of years to get permission for. I've yet to get into Coulport base, so Mam Mor trig remains in the Unreachable but Visible category (viewed it through the fence), although I've not given up hope. The other MOD UbV is Kinniny Braes; at least it can be seen across the Forth - with good optics.

Trigs are not your only interest: how are you getting on with your various other massive lists - HuMPs (hundred metre prominence summits), Ultras (worldwide summits with a 1500m prominence) etc?

For the HuMPs I have 2883 0ut of 2984 - 101 left to bag. These include a few sea stacks including the Old Man of Hoy. We're having a crack at Fair Isle's Sheep Rock this summer - it's unclear how hard it is. Simms (600m summits) - I have 2184 / 2572. Many of my outstanding HuMPs are also Simms, so bagging them tends to involve good longish outings ticking off a few summits. The Uber-list is the TuMPs (30m drop on all sides) - I have 9901 / 16853. The list includes quite a few sea stacks but most if not all of the hardest ones have been climbed by the likes of Mick Fowler. How many P30s any of the bagging community ends up with, remains to be seen.

Ultras - I have 223, in second place [in the world] behind Petter Bjorstad who has 238. Reports of my overseas ascents can be viewed here

Along with the trigs and your Marilyns first, which other lists have you already completed?

All three SMC lists (Munros, Corbetts and Donalds) and all 10 LDWA Hillwalkers Registers (including Nuttalls, Wainwrights, Birketts, County Tops etc). A recent first completion is the Haswell-Smith islands - although since HS published his book a few more qualifying islands have been identified, which a group of us hope to bag this summer.

Would it be fair to describe you as Britain's most prolific bagger?!​

Ken Whyte is ahead of me in HuMPs (he has all but 8, and has done almost all the Irish HuMPs and Marilyns) and has completed the Simms. I'm well ahead of him on TuMPs but living in England have access to a lot of smaller easier hills. Colin Crawford is also ahead of me on Simms and HuMPs and third in line with TuMPs - so he's another bagger to watch.