Your lucky at 29.9mpg av , my comp reckons im averaging 19mpg 
Tho that is on lpg mind....goes up a tad on petrol.
Tho i do a lot of town work.....av speed is usually 19mph.
Im no better off now running an omega on lpg than running a diesel.
I used to be able to get lpg for 30ppl......now im paying 59ppl
Ive chatted to a mate......who runs a VW passat 1.9TD Auto as a taxi........he works roughly the same hours a me......he bungs in £20 of diesel a day........i use £20 of lpg a day.....so no advantage to me anymore. 
End of November or sooner......my omega will be for sale.....its got until then left on its plating.....then im going back to diesel.
my nearest forecourt is BP @ 59.9
I have 2 non forecourt within 2 miles and they are both 50p per litre
Try these TD
Dieselec t/a Gas & Go Ltd, Wiltshire
Unit N, Newcombe Drive, Hawksworth Trading Estate, Swindon, SN2 2DZ
hmmmmm maybe not i have just called them and they told me it's just gone up to 58.
or calor in swindon
Bridge End Road, Swindon, SN3 4PD
Surply: Off site
Opening Times: M-F 7am-5pm Sat 8am-12noon
Phone: 01793 613391
hope this helps