"I still think we need an episode where Doctor Who sorts out his tax affairs; we still have had no explanation of his means of support and I would imagine that HMRC would be very keen to get their hands on a completed statement of assets for a start.
Sight of his completed DOM1 form would also be interesting, and it’s no good Matt Smith arguing that the department doesn’t issue them anymore, he should have completed one when he was in his original William Hartnell guise.
I’m just trying to figure out whether he would be entitled to the age allowance or not, the good doctor seems to be getting younger (bit like policemen now I think of it and now I think of it are the two somehow connected, it's a police box after all)."
- Richard Curtis on the Taxation blog.
Edit - Peter Martin has since suggested that at least we now know what TARDIS stands for: Tax Avoidance - Residence & Domicile Issues Shafted!