I am Pakistani National, living in UK. I am travelling to Pakistan via Turkish Airline. I want to go into Istanbul for a day as my next layover is 28 hours. Can I get transit visa on arrival at the airport desk?
All citizens of Pakistan require a visa in order to enter Turkey, however there are a few different types of visas available.
If you currently hold a valid/unexpired visa or residence permit for a Schengen area country, Ireland, the United Kingdom or the United States, then you will be able to apply for an eVisa, or obtain a visa on arrival once you get to Istanbul.
If you do not hold a visa/residence permit for one of those countries then you will need to apply for a visa in advance, at a Turkish consulate.
In your case, given you've stated you live in the UK, I'm presuming you hold either a UK visa or residence permit, in which case you can get by with only an eVisa. Officially, presuming you are staying overnight, you will also need a hotel reservation in advance of arriving in the country.
I would strongly suggest obtaining an eVisa in advance rather than waiting until you arrive in Turkey - it's faster, cheaper, and less likely to result in problems - you can obtain one from the official Turkey e-visa application site.