Thanks mate, got a trade card but can get the gm dexos2 for 19 quid for 5l which is about a tenner cheaper than the halfords fully synth on the old trade card
That's even cheaper per litre than Tesco's fully synth which is £20 for 4 litres - but the 8 litres you need for the change costs £40 minus the Tesco £6 off for spending £40 makes it only £34 for the 8.