In reply to mike123:
I would try Interparcel first, but if you are VAT registered you will need an EORI (easy and free) and a HS code (google it) and multiple invoice copies or whatever, even for NI, which is the course I would suggest. If Eire you would need to send 0% VAT and then they would tax them in, think.
I am sending something to NI later this week, just looks like a couple more boxes to tick but no big deal. If it was food I suspect it might be more of a big deal.
Try entering the details in here https://uk.interparcel.com/?gclid=CjwKCAiAxp-ABhALEiwAXm6IyXqV1V3irumgzlUbQ... if your parcel is too big, try 140 x 30 x 30 and 23kg, which will get you to the next stage and give you an overview of what's required.