I have worked doing the same job for 13 years.
4 years ago the company was bought out and my conditions changed hands under the Tupe regulations.
If I was to work out my redundancy years of employment, would it be 13 or 4 years?
13 years is correct. Although some conditions may change at the point of your TUPE transfer, the length of your continuous service for the purposes of employment law will definitely be transferred from the old to the new employer.