That doesn't sound like you're ready for a Lamborghini. These are definitively not meant to ride from A to B anytime as yopu would with a normal car, and you'd better know what to expect on the way...Have you given any thoughts to a Renault Scenic ?
Just joking....
The Gallardo can be a daily driver, that's for sure, but that doesn't mean it is a "real" car....no space, noise, no trunk, poor visibity (compare to "real" cars), etc, etc...in other words, it is not practical at all, and, after all, isn't it what you should be looking for in London ?
Well...I guess if you're looking for a vehicule, go for a Porsche. If you'd rather a "super cool" vehicule, go for the R8 (I love it !). If you really want an exotic, the Gallardo is a good choice, but again, be ready to live with...an exotic. Now, if you want to disappear in the mob of London, Ferrari is a good option.