Any recs for London motorcycle repairs?

My motorbike's out of action again, and it looks like fixing it will involve going fairly deep into the engine - not sure what happened, but it lost a lot of power very suddenly, oil is leaking into one of the cylinders, the spark plug seemed to be smashed, smoke is coming out (I think the gasket is leaking) and I think the piston and rings may possibly be damaged. The AA couldn't get it to run, even just to get me home, and it's definitely not going to be something I can fix myself.

A few years ago someone gave me a couple of recommendations for servicing in London, but I can't now find the entry, and I think it may be beyond the people I usually use for minor stuff like tyres etc.

It's a BMW R80 monoshock model, no fairing, so hopefully relatively easy to get inside the engine if you have the right tools. Any suggestions on someone who can service this?

Exactly what I didn't need on top of my other financial woes!

Today's charity-shop bargain...

...was Sir Howard Vincent's Police Code (15th edition), the 1912 release of the rule book for the London police, widely adopted and adapted by other police forces. It looks to be out of copyright, and there doesn't seem to be a version on line unless you're a student at Monash University, which is a little surprising.

It's nearly 300 pages with a lot of footnotes etc. but the typeface is reasonably clear, what I will probably do is try a few pages and see how well it scans, if it's OK I'll have a go at it.