I believe you are confusing the oil companies with the British government.
Whether this is a simple answer depends on your understanding of market forces and suspect futures trading practices.
The $10 a barrel rise over the last week is attributable to one rogue trader buying a hell of a lot of oil futures - this caused other brokers to think something was about to happen (i.e. a political event - war etc, which would lead to an increase in demand) and they jumped on the bandwagon too, driving the price up. When it was figured out that this trader acted on no such information, this dropped the price of oil back to $60 a barrel and lost his employer (PVM) £6million in the process.
This will also have a knock on effect in a few months time (when the 3 month futures get pumped/delivered) - they'll be a glut of oil, creating oversupply so there will likely be a drop in price as well. This is why there is talk of banning futures trading in oil.
As far as the oil price increase since the beginning of the year - the increase from $31 a barrel to around $70 is a result of the optimism that has grown for an economic recovery and therefore a rise in energy demand. This rise really is down to simple supply and demand.