The government cannot control the price of petrol, except through taxation. The wholesale price of crude is dropping, but it takes time to work its way through to the pumps. That said, I do think the suppliers are dragging their heels and I do not believe that the current price reflects the wholesale market. I would expect to see further cuts on the forecourt at some stage, although the value of sterling does not help and could be used as an excuse to keep the price higher than it would otherwise be.
As far as OPEC are concerned, you have to remember that these countries have investments throughout the world (especially the Saudis) and they are savvy enough to know that the world economy needs all the help it can get right now, so they would not, IMHO, wish to rock the boat economically. And yep, the price of crude is now down to
$61 barrel 
. I did say, back in June, that the true demand/supply price should be between $60-$80, so it's looking on the low side to me, now.
My guess (and that's all it is!) is that the price of unleaded will drift lower and bottom out somewhere between 85p and 90p per litre.