Can you apply for a 2 year tourist visa in the UK?

I can only see that a the visas on offer in the UK at the moment are for 12 months, can you apply for 2 years in the UK?

Also,

-with the 12 month one, do I have 12 months to enter China if my application is approved?
-once in China, can I stay up to 12 months, so for instance, I receive a tourist L on 1 January 2015, I can enter China on 31 December 2015 and leave China on 30 December 2016?
-can any British passport holder apply for this 12 month one, since I have been to China previously (on my former passport) and had one month and also double entry ones previously?