Under English law consideration needs to be paid to make a contract valid.
The reason for that is that both parties are meant to get value from a contract, it wouldn't be enforceable otherwise.
So paying £1 ensures that the party who for e.g. assigned their intellectual property to the company in an IP Assignment agreement is getting something in return (i.e. £1), they're not doing it for nothing.
So the contract included wording to say that, in this case, the company agrees to pay the other £1 at the time they sign the agreement, and the other party agrees that the £1 has been received by them.
This consideration, as it's known, used to be a peppercorn, now it’s a pound – some fun reading here.