In message , Saint
writes

Well I got lucky todat in the respct that I found a shop open who took a
look at it. They agree that the noise is the bottom bracket but say that
it's clean, greased, fitted and tightened properly and the problem may be
that it is just 'bedding in'.

That's the second shop telling me that there's nothing wrong but I don't buy
it at all - you don't buy a new bike and expect it to make such a din - it's
maddening when riding.

Is it difficult to fit a new crank? Does it involve removing the frone mech
et al? Are there special tools needed?

Just before you spend any money, check the seatpost is greased where it
sits in the frame (unless it's carbon) and the saddle clamp is cinched
up tightly, both can cause a creak that can sound a lot like a bottom
bracket, especially with an aluminium frame.

To check if it is this, stand up and pedal, if the sound goes away then
it's probably that, if not then look at the cranks again. With creaks
it's a long process of elimination, but check each set of bolts in turn
until you find what has affected it. Also take a look at your pedals,
seen a spd style pedal creak a bit like a bb too...

To be fair both shops should have told you this, trying each bit in turn
until you don't get the squeak, the mechanic really should have taken it
for a test ride for such creaks, or even ride along side you to see if
that helps.

Then chuck money at it

--
Thomas Letherby