I thought it wasnt possible to fly commercial single engine IFR Operations in the UK.
It's not...I have seen some PC-12's being operated but I believe they are under private ownership and probably not on an AOC. Some JAA states do have an exemption to this rule though.
I understand that to fly single pilot multi-engine IFR public transport flights (ie air taxi) there is a requirement to have something like 700 hrs total time with 100 multi?
It's not mandatory, I was considering an air-taxi job a while back and the requirements were 300TT 100ME. I don't know whether the company needs to seek permission from the CAA to do this but I think 700/100 is unrealistic with the JAA system in place.
Best regards
MP