Yep, HMRC enforcement officers have right of entry... and probably more powers than the rozzers when it comes to investigation.
My TV Licencing story: about 15 years ago, I moved house... did the proper thing and filled in a change of address on the TV Licencing website, got the confirmation that the record had been updated and thought no more about it.
Few months after we'd moved in, the "you don't have a licence" letters started coming - ramping up in tone from "we don't think you have one, if you need one get one please" to "you're going to court for a £1000 fine". On the basis that there was no cost free way to say "I have a licence, please sod off", I ignored the letters, but kept a record of everything.
Six months later a summons to the local magistrates court for non-payment of TV licence... so I turned up, with 14 years of licences and the confirmation of the change of address on the last one. Listened to the charge and then when asked how I pleaded "not guilty".
"What evidence do you offer in your defence?"
"TV licences going back 13½ years with 6 months to run on the current one"
"Why did you not do this before?"
"Nobody has actually directly asked to see it, only threatened action and I assumed this database that TVL adverts make a song and dance about was actually something close to correct"
<Strangled silence from TVL legal man>