I'm not a TUPE or legal expert, but if I was in your position I would just assume that the newly transferred staff are covered by TUPE. Unless your new staff have said that they do not want to work for your firm (ie they have resigned), you will probably need to treat them as if they have worked for you since 2007. Even if they maintain their employment with the old company on other sites, it is probably irrelevant from your point of view. Regardless of what the law says, as employers I think we have an obligation to treat our staff fairly. Why don't you just avoid the hassle and potential unfair dismissal penalties and just offer two of the cleaners redundancy or alternative positions in your company? I believe that they would only be entitled to 1 or 1.5 weeks gross pay per full year worked. Perhaps you should just put this one down to experience and move on.