I would recommend keeping what you have for now. However just to play devil's advocate and look at different options.
I have taken your monthly commute and your average MPG and worked out roughly your fuel costs:
Miles 1600
MPG 45
Gallons 35.56
Liters 161.64
£/Liter 1.34
Cost: £216.60
If you buy an old second generation Hybrid you should average 60 MPG (from my own personal experience, I had a 2008 Pirus).
Miles 1600
MPG 60
Gallons 26.67
Liters 121.23
£/Liter 1.29
Cost: £156.39
If you have a driveway or a garage, then you could also consider an electric car. The car would cost more to buy, however be a lot cheaper to run. The below figures are based on my current car with your commute.
Miles 1600
Mile Per Kilowatt Hour 5.0
Total KW/h 320.00
KW/h Cost £0.12
Cost: £38.40
If you can charge with cheap electric overnight, instead of during the day, then you can basically half the electric cost quoted above. In my case I actually pay £0.05 per KW/h overnight.