Hi,
Jewsons in Cringleford Norwich will hire you one out. Just make sure if it is a Howdens kitchen the jig has the capacity for a 616mm worktop as all theirs are, unlike everybody else who use a 600mm worktop.
When you glue and bolt the worktops for the first time it can be stressful, so make sure you have everything to hand. It is also helpful to have two of you when doing this, one underneath with the spanner and one on top "adjusting" the joint.
Another good tip, when your mate gets the worktops lay them flat until ready for the install. The reason I say this is I done some a couple of weeks ago and the worktops had been stored on their side and curled which meant they were a right PIA to get right.
Envy you living on the broads, fitted a new houseboat out in Brundall last year including a new kitchen, and it was a refreshing change to the norm working on water.
Good luck with the worktops.
Cheers,
Mark.