If you spent 45 or more years working, then you may have changed company numerous times in your career.
Do you know where all your old pension schemes are? Some reports indicate that over £5 billion in pensions are going unclaimed in the UK.
Many companies out there offer to find all your old pensions for you, however they are going to charge you an arm and leg for doing so. You can do it yourself for free (and so can some pension providers upon purchase of post retirement products. Make sure you ask for this service if you are at this stage).
Use this guide from the Money Advice Service to trace lost pensions and request forecasts for their values. To save you even more time, they have even provided letters for you to use in your requests.