Should I get an annual statement of my state pension for my tax return?

http://www.hmrc.gov.uk/manuals/eimanual/eim76005.htm
"Payments not made weekly
Claimants can choose to receive some benefits (for example, the State pension) every four or thirteen weeks in arrears, rather than receiving the benefit each week.

Depending on payment dates, an individual who chooses to receive the State pension every 4 weeks in arrears, may receive 14 payments in a year (equivalent to 56 weeks benefit) but for income tax purposes the individual remains taxable to the 52 weeks pension entitlement that arose during the tax year ended on 5 April.

In the following year the individual may receive 12 payments equivalent to only 48 weeks entitlement but the taxable benefit will again be the 52 weeks entitlement.

The correct taxable amount is always the figure of weekly entitlement."

No need to make it too complicated. The letter you get each year tells you how much you will receive per week for the forthcoming tax year.

You just need to multiply that figure by 52 to get the annual amount, no matter whether you actually receive the money 4 weekly or weekly.