prices go up, prices go down. Most likely in 7 years (or 5, or maybe 3) it will have gone up quite a bit from today's lows. Today would be a particularly bad day to start drawing on your pension because the fund value is almost certainly lower than it was 12 months ago, or 6, or 3, or 1.
IMO this is a good time to leave the fund to grow.
However, at any time after your 50th birthday, you can start taking income from some or all of your pension fund, and a tax-free lump sum. From memory, if you are 55, you can draw an income of up to 7% p.a. of fund value. However (1) today the fund value is low due to the markets subsiding (2) if the fund does not grow by 7% or more each year, its value will be eroded because you will be drawing more than it earns.
As a basic rate taxpayer, your pension contributions do not get such a substantial rebate as they would if you were a higher-rate taxpayer (or a non-taxpayer) although contributions receive a rebate of the income tax you pay (the principle is, untaxed when they go in, but taxed when they come out). Some people would say that because prices are low this year, this is a good time to buy, as prices will be higher in a few years. Unfortunately our gut feeling leads us in the opposte direction.
If you have your own company, you can get an extra benefit if the company makes the pension contributions, rather than them coming out of your wages, because they are then not subject to Employers NI which is about 12% this is a good deal, because it means that each £1 going into the fund costs less than 70p out of your pocket (tax and NI).
If you are an employee, and the company makes a contribution to match your own, get as much as you can of their money.