UKH

I have a rather old MTB (2008) and need to replace the 26" tyres, which are currently 26x2.0, at a push I could probably fit 2.1 although I know not all tyres are created equal. I currently have a very old pair of Specialized The Captain, which I have to say I've had no issues with.

Seems 26" doesn't give you the best choice in tyres these days. Is anyone able to recommend some? Looking at mostly forestry trails/ some moor/dales tracks so semi hardpack/gravel/rocky/rooty/light mud and puddles not much tarmac but like cycling up as well as down so not too sloggy! Would tend to avoid full on mud. 

any suggestions would be really helpful

Panaracer XC pros used to come up quite narrow if that's what your concern is.  A set of Fox 32 forks will allow a 2.4 Rubber Queen (now called Mountain King) with room to spare

If you go on to a well known online shop (chain….) and use the filters you’ll get to see what choice is left. Except that supply generally for bikes and bits seems to be stretched very thin at the minute.

I fitted a Continental 2.4 inside a very old set of Marzocchi forks a few years ago, no bother.

https://www.cyclestore.co.uk/specialized_ground_control_control_2bliss_read...

26x2.1 folding bead and decent rubber compound, also tubeless compatible. Should be ok for the type of riding you describe being a XC/Trail tyre. 

Schwalbe blackjack 1.9, not brilliant in mud but OK for most surfaces and seem to me to not be too draggy.