I found but have now lost a web-site which has details of UK death registrations for recent years (e.g. 2012). Can anyone help please?

As far as I am aware, GRO Death Registrations for England & Wales are only available online up to 2007. You can obtain more recent information but only by making a personal visit to one of the seven repositories listed on the GRO web site at https://www.gov.uk/research-family-history . However, if the deceased left a Will or if Letters of Administration were obtained, you can search the Probate Registry web site at https://probatesearch.service.gov.uk/#wills and the results will show the date of death. The search is free of charge. This site is up-to-date, so probates granted this month will be shown. Best wishes, Marion Woolgar Bognor Regis, West Sussex SFHG Member No: 3323