Talk to your local radiator specialist mate. I used the Yellow Pages to find mine. Was pretty steep but that's because I'm in NI. Did a good job though.
you could have a blown headgasket, you could have cracked block, or a cracked head.
i would recomend taking it to a trusted mechanic, get a compression test done, also there is a test where they pressurise the cooling system to see if there is a leak, and there is a dye they put in the coolant to see if its the headgasket.
go to a mechanic fella there is no point in speculation, it will just make you worry.
to test the head for a crack it must come of, it goes to a machine shop to get done but worth the money if it goes on again same happens again you get double the repair bill plus having to buy a new head. check for a creamy gunk in the oil that indicates water in the oil which means water is leaking into possibly the cylinder and/or oil hole back to the sump andul find it buy taking out the dipstick check the coolant bottle for the same thing.