I am not sure if there is Citi in UK... if so, open an account there, and have them also open an account in Singapore (someone said this can be done remotely with Citi). I am not sure if HSBC has a similar perk, if so, it may be best to use that.
For the flat, I hope you have somebody here in Singapore who you can trust who viewed the flat for you and sent you pics. Ideally, this would be a friend you trust with the money so he can receive the deposit. Otherwise, it may be better to come here first, depending on your comfort level.
For transfers BEFORE you arrive (to transfer the money to the agent), if you cannot setup the Citi or the HSBC account pair, the best may be to use Western Union or similar, it's fast and reliable, as long as you can trust the money recipient