Buying a bike in the UK?

I'm headed to London next month with the intention of buying a bike to tour Spain, France, Italy. Currently, I'm browsing ebay.co.uk, motorcyclenews.com and gumtree.com
Can anyone recommend other classified sites for used bikes?

Also, can anyone recommend an inexpensive insurance provider?

And what are the steps for registering a bike there?

thanks in advance

Matty

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