Petrol (and diesel) prices can vary considerably. As of 30th August 2016, the cheapest price for unleaded is 105.9 pence and the maximum is 129.90 pence. Of course there is quite a variance across the UK but even in your local area, the price difference can soon add up.
Sign up to PetrolPrices and they will send you a weekly email. This will show the chepeast 5 fuel stations nearest to your chosen address (you set the search radius). You can also add two other postcodes (e.g. work and somewhere else).
The amount you can save by shopping for fuel smartly will amaze you.