After a little bit of drama, the worktops are done.
If you only do this now and again you can hire most of the kit, you'll need a decent router, 30mm guide, jig, clamps and cutter (you'll have to buy the cutter ~ £15). Hire of router and jig is around £40 (weekend rate). The router needs to be 1/2" collet.
The jig has about 1mm play so cut 10mm at a time holding the router away from the work until the waste is removed then make a final pass holding the router towards the work to clean the cut up.
It's a very unforgiving process so measure, measure, measure lol. It ends up with 90 degree joints and your kitchen won't be square so cut over-length and juggle for square before making final cuts. Most times it's easier to chop a bit of plaster out so you can juggle the worktops. You can lose a 10mm gap at the wall with tiles or splash-back board in any case.
Obviously, since it was MY kitchen I had to mong one joint, hopefully not too noticeable!
Read the jig instructions carefully,have a practice on some scrap pieces and all will be fine