Surely some mistake?

Dear Ms Asif

Surely some mistake? Didn't you mean to send this letter to Vodaphone, or Goldman Sachs?

Ah, no - my mistake: 'criminal proceedings ... we have arrested ...' - that wouldn't be million- or billion-pound tax-evaders (oops! sorry - 'avoiders') then, would it? No, that would be plumbers. Who, whatever the press claims, aren't quite in that league yet.

So, you're identifying the plumbers you'll be investigating next.
You're cross-referencing your data with trades bodies and merchants.
You're matching the materials plumbers purchase for their jobs with the work they have declared which will show up any differences.

And how much work is this taking? I mean, suppose I change a tap for Mrs Boggins: do you have an army of tax inspectors going through the sales ledgers of all the plumbers' merchants in my area matching up what they've sold me with what's on my tax return to ensure that I've declared a payment from Mrs B that matches the tap sale? (How much do tax inspectors cost these days, anyway? Not just their salaries of course but the true cost of employing them.)

And how much unpaid tax do you expect to identify, let alone recover?
(OK I guess the last two figures are much the same, even if you have to sell the plumber's house from over his head and throw his kids out on the street. I mean, it's not like he's Goldman Sachs, or Vodaphone, or anyone who matters, is he?)

Anyway I'll be extra careful from now on. Next time I crawl back late in the evening, tired and dirty from fixing the Cratchit's clapped out old boiler (costs them a fortune to run but they can't afford a newer, more efficient one) with a slim bunch of dog-eared tenners in my pocket (not half what the job's worth but you can see their family's struggling with the government's austerity measures already: jeez, what couldn't a few billion quid do to help out the poorer members of society?) I'll make absolutely sure I sit straight down and declare it in my accounts so I pay my tax on it.

Happy now?