[Neil Jones]

Precisely 1st January 1988 when frontcaps were dropped (sometime during 1983 when they were ditched during CITV) - though I think YTV had a practice of retaining their Liquid Gold ident for most, if not all, network output (even if the ident itself was bypassed)

Here's an episode of Supergran from 1985 with Tyne Tees ident:
www.youtube.com 

As this was a Network DVD (and the video must have come from a DVD as it would be almost unheard of for an endcap to stay on air for 15 seconds even in this era of Children's ITV), its probably faithful to the original programme, as I don't really see why Network would go to the trouble of getting the right front cap for the right era just for a DVD release?

IIRC Children's ITV programmes still had front-caps, but weren't played on air, though the Tyne Tees example suggests they were probably present on the programmes until some point down the line...?