Whatever the decision, I cannot see it leading to a reduction is petrol prices on the street.
As people have said before, its happened many times before, especially in the technology world. One that sticks in my head is the price fixing of LCD panels by pretty much all the major manufacturers, it didn't result in super cheap quality LCD panels afterwards.
They WILL be found guilty, they wouldn't be investigating if they didn't have a reasonable cause, they will get a massive public shaming, a few top nobs will loose their jobs, someone in the government will also be found guilty of aiding and abetting as well, the oil companies will get a fine, new laws will come in and petrol will still stay well above £1.00/litre.
Also (but mildly off topic), can someone explain to me why I get taxed on my pay, then the government tax the fuel which increases its price to me, and then they add VAT onto this fuel. Why am I essentially taxed 3 times to buy a litre of fuel?