It is worth buy? Absolutely!!
I predict (confidently) that there will be a double dip.
Obviously, the share price will continue to fall over the coming days/weeks - I would be tempted to buy at around 350p. As soon as the leak is fixed the price will rocket up (to maybe 390p to 440p - from there it will float at around 475p. At this point I would sell half of the shares.
Then wait until the court proceedings start and an announcement of the fine is released - I would expect in the region on £7bn to £10bn of provisions in their 2010 R&A - This announcement will obviously push the price down considerably to around 375p. I would then buy again and hold on till it reaches 550p to 600p (obviously hold on for longer term investment).
All in all it would a medium term investment. If you're looking for a quick profit, then basically do the first step.
The reason I am so confident of this is because, ironically this event will help oil companies, as it will push up the price of oil in the medium/long term. Over the next couple of years there will be serious restrictions over offshore drilling in the US. This will lead to a significant rise in the world's oil price (close to 2008 prices).
In addition, I would recommend splitting your investment between BP and Exxon. Part of the reason that the US is "up in arms" is because it's a non-US company which has done this. Believe me, if Exxon caused this problem there would be a lot less political uproar.
Nevertheless, Exxon will profit from BP's short term issues - whilst, they will run into problems themselves, over offshore drilling plans, they will be given more favourable licensing than non-US companies. In addition, my comments about the oil prices rocketing up, will lead to Exxons share price to increase significantly over the coming few years.
Long winded I know, but I hope it's useful and CORRECT!