I am no pensions expert, but there are many factors that will render any figure given today (presumably many years in advance of your actual retirement) as extremely wide of the mark.
Basing my answer on the current financial climate, and assuming the income will come from an annuity and not drawdown, I believe you are currently looking at a 'pot' of around �400,000.
Just a note about the apparent disparity between Kempie's answer and my own. Kempie's answer is probably the most accurate if you're hoping to retire (at 55) soon and just want to check that your pension will meet your needs.
My answer was based upon putting some sample data (for 20 or 25-year-old males) into the calculator to try to achieve a pension EQUIVALENT to �30,000 (at today'sprices) at the date of retirement. Most data I put in suggested that you'd need about 31.3 times the required pension value, hence my answer.
This is something that I have been looking into recently due to possible redundancy and have been quoted approx 400t to be in the pot to pay approx 1700-2000 per month nett at age 59. (age now 58.5) hope this helps.