There are a couple of problems with trying to work at MAN or any UK airport for that matter.
Firstly is getting an airside pass, you need to be an employee first off, yes you can get temporary 1-5 or 60 day passes, but once you have had one of these you can't get another for 2 months.
If you were fortunate enough for someone to agree and get you a permanent pass, you will most likely have to pay for it. Plus the basic disclosure etc.
Secondly, insurance, if you are not an employee then you won't be covered under the companies liability insurance, unless you have personal liability insurance that covers you for damge/grounding an aircraft to the tune of $20,000,000 + then it becomes impossible to let you near an a/c.