In the words of good old Victor Meldrew 'I don't believe it!' or rather I didn't believe it!
For around six years I have bought my petrol at the same petrol station because it is usually one of the lowest prices around where I live. I drove past on Friday and their 4 star was priced at 115.9 - on Saturday when I drove past it was 120.9 - a whole 5 pence per litre overnight. Needless to say I will be looking for an alternative supplier and suspect there will be a number of others who do the same - there is another petrol station about half a mile away where it has just gone up to 115.9 so looks like that will be where I will go next time.
The ironic thing is that the petrol station that has upped the price has run out of petrol while the cheaper one still has both petrol and diesel.