Normally I'd start by recommending PayPal as the cheapest way to transfer money overseas but the absence of a bank account might make that difficult (or probably impossible). Here's the link anyway:
https://www.paypal-ma...k/sendmoney/index.htm
My next choice would normally be iKobo (which I've used loads of times myself, and can recommend) but their website says that transfer services are temporarily suspended. (It's unclear as to whether that's a for a few hours or for a few months!). Here's the link anyway:
https://www.ikobo.com/
Other than those services, you're basically left with Moneygram (see Craft's link) or Western Union:
http://www.westernunion.co.uk
Alternatively, you could change the £400 into Euros (at the Post Office) and then split it into 4 equal payments of (the equivalent of) £100 each, which is the maximum amount covered by insurance if you send cash by the International Signed For or Airsure postal services:
http://www.royalmail....0948&mediaId=13300215
Chris