Just wanted to add another (plumber) recommendation for Chris W. in this thread. The best one we've come across so far in our 15+ years of London-living.
Pulp salon in Crouch End used to do 50% off cut and highlights during weekdays so it's worth checking if the deal is still on. I've been going there for a few years and have only had a dodgy cut once and they seem to specialise in highlights.
That pool (at South Harringay School) is used for babies/kids' swimming classes on the weekends and the pool is quite small. Probably nice for floating around but not so much for full-on exercise...I didn't realise it was open to the public.