Your best bet might be to register your trademark with doubleclick, then lodge a complaint against your competitor using your product/company name in their advertisements.
We don't own the trademark (I mean, we never registered it officially). Since we are small, we are putting our money on things that we thought mattered more.
In the US, registering a trademark (which you can easily do yourself - no need to pay a $300/hour lawyer) costs $75, or at least used to last time I needed to. How much is it in the UK that you're saving that money?
I guess we will have to register it.
thanks for the tips.