About a month ago i ran a spur to feed a socket in my garage,after
connecting and checking i switched on mains supply.

Did checking include measuring the continuity (with a specialised tester
that provides 200mA of current), insulation resistance (with a specialised
tester that provides 500V DC) and earth loop impedence (with a specialised
tester that pulls 20A down the line)?

If not, obtain said testers (or an electrician) and see what the results
are.

Christian.