When did U.K schools have guards? ?

Not in most areas, no they do not have guards.  Where are these?

I really like it. Guards and cctv have made schools much safer. The other answers from people obviously aren’t old enough to know.

Why ask a question unrelated to history in the History category.

Pick Education or Current Events 

Maureen Cobbett, headteacher at The Latymer School in Edmonton, north London, has warned the children are being targeted at the school gates.  

One of the country’s leading grammar schools has hired a security guard to protect pupils from a spate of muggings....

State schools don't usually have guards, but for years private schools with the potential for kidnapping/ransom have had their own security. It all became an issue after the Dunblane Massacre in 1996 and Schools are required to undertake risk assessments accordingly.