There is a pension tracing service on gov.uk website. Here is an excerpt from the website.
"Use this service to find contact details to search for a lost pension.
You can find contact details for:
your own workplace or personal pension scheme
someone else’s scheme if you have their permission
This service will not tell you whether you have a pension, or what its value is.
You need the name of an employer or a pension provider to use this service."
https://www.gov.uk/find-pension-contact-details