For the Dutch people, try getting an EasyJet-flight as RyanAir is extremely shit. Aswell keep in mind you need enough money for public transport, as most of the budget flightoperators will fly towards the smaller airports at the border of London. Be advised that travelling in London is recommended with an Oyster-card, something compared to the OV-Chipkaart but better.
If anyone got questions, from the Netherlands or other countries outside the UK, just ask me. I'm a regular traveller through Europe (by train and plane) and I might be able to help you out.