Managed to do a few more things on the GTI;
Replaced the PCV, fuel filter and spark plugs all genuine parts. Does feel smoother now. Although the mechanic struggled to get the fuel lines off the old filter just hope he didn't cause any damage or leaks.
MPG wise I am getting about 30-34 on my 9 mile commute to work mix of traffic and dual carriageways. £30 of V Power (~22 litres) gave me roughly 135 miles so probably not too bad.
Next is to investigate the rear calipers and getting a whirring/booming noise which changes on different roads. I am thinking of getting the alignment done again and checking the state of the tyres.