I was reluctant to name the garage in negative comments - i can't remember z4-forum rules. but yes, it was Technosport. Nice guy, meant well - but couldn't diagnose worn follower fingers and instead just billed me for a completely pointless valve shim job. Whilst waiting in the carpark i also spoke to two other customers that were having a complete mare with their cars there too. i took the car elsewhere. Honestly given 5 minutes with the cover off i'd of seen it, so no idea what he was doing. In comparison - one of the junior guys at CPC put a dowel against the engine, listened in a few places - and told me it was worn fingers before even taking a spanner to it.
Needless to say i have a bag of them here somewhere (because they're £900 to replace, i'll find something to do with them one day...), worn in various degrees, the worst one is my keyring. FWIW i believe this was caused by a BMW stealership in the tunbridge wells area not doing a proper valve shim job on the s54. Luckily i had an ear for the noise change before it caused any problems to anything other than my bank balance.
I can completely imagine the slightly odd business practice i mentioned being interpreted as bad customer service at CPC PE - as in - it's sometimes hard to get hold of them (because the receptionist is more available during the morning.. so you wont get fast responses in the afternoon), and they shut early.
If it's any use, i'd completely avoid BMW Park Lane (they used to have two workshops in battersea, i think one workshop is now up near wembley....) - i can go in to details, but if i just say i have £thousands worth of compensation from them (actually my old z4m's new forum-member-owner is a beneficiary of some of it now, i think) you'll know enough to avoid
and that's despite being owned by BMW UK and having access to the BMW UK senior master tech guys.