Well it is possible to get one, as I did a couple of years ago.
However, the major difference was I contacted HMRC first - rather than they contacted me.
I originally contacted then through their web site...
http://www.hmrc.gov.uk/cnr/& then they contacted me via my e-mail address.
After much 'to & throw' between us about things like my National Insurance number, date of birth, place of birth,where I had work, P60s & the like for the previous 5 years & current pension details they eventually said they owed me money. They also sent me a great deal of detail through the post showing how the tax liability for the last 5 years had been worked out.
They then asked me for my bank details to repay me....
Now I must admit that freaked me out a bit. I am not happy about giving those sort of details out.
So I found (via UK Government sites = .gov) the telephone number of the tax office in Nottingham (who deal with these 'overseas' claims) & telephoned them.
At first they were dubious that I had received a letter from them...however after a bit of research (I talked to the person who had written it) I discovered it was genuine.
They offered me 2 other ways of confirming my bank details.
Via air-mail letter to the address that was on the dot.gov web site.
Via a fax to the fax number quoted on the dot.gov web site.
The money was paid into my bank account no problem.
My point is that I would certainly NOT send them any details without confirming (by independent means) that they are actually who they say they are.
For example, do not click on any link they send you - Google for the Government site independently.
The same with phone & fax numbers.
While talking to the Tax office they did say to me that many people were caught out by scams like this. No one was slightly put out that I was 'checking up' on them & that was after something like 8 e-mails between us..