Yes and No.
It depends where you spent the money. It depends on your residence status in the UK. It also depends on the definition (under UK law) of the withdrawal (lump sum or annuity). The US/UK treaty also affects it.
You don't have to pay tax if:
You weren't resident in the UK.
You were resident in the UK, but did not remit (spend) the funds within the UK. This is a matter of some debate, since the US/UK tax treaty claims that the country you are resident in has first right to tax.
You were resident and remitted the funds to the UK, but they meet the definition (under UK law) of a lump sum distribution from a foreign pension. Under the US/UK treaty, it's a pension. Under US law, it's a Partial Distribution, which is neither a Lump Sum nor an Annuity, but rather somewhere in-between. A good argument can be made that it is a lump sum under UK law, since it isn't repeated annually. As a lump sum, it's tax-free. An argument could be made that it isn't a lump sum under the spirit of UK law, since a lump sum under UK law meets very specific guidelines as to being 25% or less of the total value of the assets within the fund. If the $8,000 represents more than 25% of the total value of the fund, there is some cause for arguing that the payment is subject to UK tax. If so, it would only be on 90% of the $8,000, rather than the full amount.
In short, I think you can find many arguments to leave the US IRA distribution off the UK tax return; but you should probably have a UK tax accountant prepare your return who would be willing to argue your case should your return be selected for an investigation. You should never argue your own case - it's rather like defending yourself in a court of law; even lawyers hire other lawyers to do that for themselves.