Hmmmm - There are a lot of Aussies in Earls Court. Head to a bar, listen for some accents and then introduce yourself ;). You may not want to mix with Aussies (cos you're on holiday and you want to meet others.......), but they will welcome you in and give you some fresh local tips on what they did to meet people.
I also did a couple of walking tours around the city, nice way to meet people but mostly my groups tended to be older and in couples. almost 8 years ago
Go and stay in a hostel, preferably in a dorm room. You have no choice but to meet people! It might seem scary to start up a conversation with strangers, but remember that nearly everyone is in the same boat. Find someone who looks like they're travelling on their own. Hi, what's your name, where are you from? what did you do today? ... Can I come with you tomorrow...? almost 8 years ago