Well I've done it!!! and, if I do say so myself, it looks great :-)

First time I've had to use a router for lots of cuts on thick (40mm)
oak and it was hard work - my router was easily up to the job (a Trend
T11), but I wish I'd known how quickly oak seems to blunt the cutter,
I only had one 50mm cutter and could really have done with 2 (or 3)

In the end it took 2 days because I kept making templates and jigs, I
wanted to get nice curves on the pipe cutout and to put a
not-quite-radius curve on the exposed end

It's all dry fitted - not screwed into place yet as waiting for a
delivery of some Rustin's to oil the wood. Once I've applied a couple
of coats to the bottom and back I'll be able to fix it down and then
carry on applying oil to the top.

A quick question, if I may - the worktop doesn't have any cabinets
underneath, but does have a washing machine and tumble dryer
(externally vented), there's about 30mm clearance between the top of
the appliances and the bottom of the worktop and there should be
plenty of air circulation. Given that I'm going to apply a couple of
coats of oil, is it worth fixing a vapour barrier (?plastic sheet?) to
the bottom of the worktop in the area above the appliances?

Perry