Very, very broadly, to get 12 k a year (presumes8k of state pension) and retiring at 67, I’d say at least £1500 a month. That would get you a pot in an aggressively managed fund of £250k. Not sure on second thoughts that is enough and I’d be wary of aggressive management at 54, most people ease up a bit as there is less time if things go Pete Tong.
If you are worrying about pensions, try the pensions board on Money Saving Expert forum. Some very knowledgeable and helpful people there.