OP, you have been given some solid advice from a knowledgeable group of people. You can choose to heed it, or not, but, having worked in the UK, I can tell you that the chances of you working without proper documentation is virtually zero. The penalties to the employer are too great for them to risk it. I'd also consider a different immigration "specialist", your guy sounds more like the type to put you in the back of a lorry in Calais.