Expenses for nights on Agency work

pierrot 14:
Can I put a new twist to the discussion ? The agency I work for pay us travel expenses, the amount relates to how far the client is from where we live. £6 for local ones and £15 for those outside the area. Now this payment goes down on our pay slips as “travel” and doesn’t get taxed. The agency says that its a way to get us tax-free money.
2 questions, is the agency scamming me? Can I still claim mileage from HMRC?

How can you claim from HMRC when you live in France?
If you live in the UK, would 40p per mile cover how far you travel to get to work?