I’ll let you in on a great secret on affordable London accomodation. This won’t be a secret to anyone who has spent a considerable amount of time in the UK, but almost no one in Australia will have heard about them. It’s the Premier Inn Hotel chain. They are a no frills style hotel, but the beds are comfortable, rooms a decent size and very clean. They are all over the UK and they are all basically the same design. If you pay up front and well in advance you can get so utter bargains. We are staying in Hammersmith in West London, right near a tube station on the the Piccadilly, Circle and Hammersmith lines, so it’s super central with easy access to Heathrow and other parts of London. Breakfast was included in the rate, and it was £58 (~$120) per night. There is zero chance you could find accommodation of this quality in an equivalent part of Sydney for that price. Premier Inn are everywhere and rates vary per area (they also have cheaper capsule like accomodation). Prices will be more if you book later or during peak times, but there are bargains to be had. A night in London won’t necessarily bankrupt you.
The reason no one much outside the UK knows about this is they don’t open their booking through the usual aggregator sites like booking dot com.
Is there any downside ? Not really but they don’t really have flexible rooms. They are all double bed rooms and will let you have a rollaway for a kid, but anything else you need to book multiple rooms.
https://www.premierinn.com/gb/en/home.html
It's all about the coffee 