tupe is usually an issue on larger accounts, the chance of this been an issue on yours is unlikely.
I would go for the job, and see if the cleaners is tupied over, unlikely.
If they are you could offer a payoff, this is not as expensive as you might think, it's only one week per year of service, and if you have decent terms and conditions in your contract you should have made this the cost of the client not you.
if you need to discuss this issue give me a call 07833439686.
basically, go for the job...suck it and see