DON'T DO IT!!!!
This is a scam. At first it looks OK but closer inspection and there are obvious signs that it's not from whom it purports to be:
Generally be cautious about releasing any personal or financial information online without checking the bona fides of the person or organisation who requests it.
If you become the target of a bogus HMRC email scam you are encouraged to report it to them -just forward to this address: firstname.lastname@example.org