1. Not in my experience. The OR asked for some details about my previous employment when I had the call with her, but didnt go into any great detail with her questions and didn't contact them. She wanted to know what they did, what I did there, and what salary I earned - that was it. I think they will be more concerned about what you're working at now in the UK. Even at that, they didn't contact my current employer, so I would guess that once everything stacks up and you give the OR sufficient proof of your employment in the UK they will not contact anyone looking for more information.
2. Not sure, but mine hasn't said anything about it if they were contacted. As long as you have bneen a good tenant I see no reason why they would revoke your tenancy. Check your lease - mine didnt actually say anything about it. The OR will leave you with enough money to pay the rent, etc each month, so can't see what the landlord has to lose by keeping you on.