I really would not want to have all the hassle and fuss of coming home and finding the car damaged or gone. My car was worth considerably more than £150 and I just would not want to take the risk. Anyhow your car belongs to you and not to me. Whilst I agree that Parking at Heathrow is ridiculously expensive, it is trivial compared to the value of the car. You may consider Egham safe, but I would not park in any residential street with all the aggravation of " you're parked outside my house!" and being hemmed in as happened to someone I know. Whether it is legal or not is almost irrelevant, I prefer to stir up other hornets nests. Once you start parking outside other people's houses with their imagined right of location, matters get very personal very quickly. I simply would not do it.