Because of the U.S./U.K. tax treaty, U.S. citizens with U.K. pensions can deduct contributions from income to their U.K. pension just like they could for an American 401 (k) or similar retirement vehicles.
There will not be a place in TurboTax for this situation. I would suggest just entering it under IRA and keep records of what you did in case it is questioned. You will have to pay with the entry to be sure you get the right outcome.
For example answer No to having a plan at work, even though this could be a work plan. Someone else will probably have a better solution for this. You want to take advantage of the tax break for making these contributions. Entering as Traditional IRA is my best thought for this.
Per Article 18 (5) (a) of the US-UK tax treaty:
In order for a US taxpayer to deduct contributions to a UK pension plan, the taxpayer must be living and working in the UK.
I am assuming you are a U.S. citizen.
Here is the exact wording of Article 18 (5) (a):
5. a) Where a citizen of the United States who is a resident of the United Kingdom
exercises an employment in the United Kingdom (emphasis mine) the income from which is taxable in
the United Kingdom and is borne by an employer who is a resident of the United
Kingdom or by a permanent establishment situated in the United Kingdom, and the
individual is a member or beneficiary of, or participant in, a pension scheme established
in the United Kingdom,
(i) contributions paid by or on behalf of that individual to the pension
scheme during the period that he exercises the employment in the United
Kingdom, and that are attributable to the employment, shall be deductible (or
excludable) in computing his taxable income in the United States;
All I can do is cite for you the information that I believe is relevant to your situation. What you do with that information is of course up to you.