Found out what the creaking was already! The rear wheel bearing has broken open – after only 9000km on a wheel costing £800!!!!!!! Left it in a bike shop for them to have a look at it overnight. I only spotted it because of cleaning the bike prior to a workout – they always say this is one reason you should clean the bike after every ride.
Ended up going for a ride on the mountian bike but my energy levels were too low. Still managed 255 Watts on one section of climb but my heart rate wouldn’t go up. Kept the workout short and returned to base. Not experiencing any real d.o.m.s. from the last run a couple of days ago – so that’s a great sign, but legs are still a bit tired from the really hard session on Saturday up to Notre dame du Pré – best to let them recover properly – after all that’s how they get stronger.
(The following Spring I find that one of the pedal cranks is not properly tight – so the creak probably actually came from there. I do my own maintenance now and have bought the required tools!)