http://www.legislation.gov.uk/id/ukpga/2014/19/enacted

Part 1State pension

State pension at the full or reduced rate

3Full and reduced rates of state pension

1

The full rate of the state pension is the weekly rate for the time being specified in regulations.

2

The reduced rate of the state pension for a person is the following proportion of the full rate—

\frac{1}{35} \times the person's number of qualifying years.

3

Once the full rate has been specified, the power to make regulations under subsection (1) may not be re-exercised so as to reduce the rate.