the truth is that this is a scam, did you honestly ever expect someone to email you saying you've won half a million pounds in a lottery/ prize draw etc which you never entered? As you have now contacted them back, your contact details will be passed around to other scammers trying to get money out of you.
Rule 1 - You CANNOT win a lottery in the UK if you don't buy a ticket. Not ever. Not in the UK, because it is against the government gaming rules. You cannot be entered for a prize draw with your email address or phone number or car registration or anything else. If you are entered into a lottery it is because you have paid cash and bought a ticket to do so. Anyone who tells you that you've won something without you even knowing is a scammer.
Rule 2 - Get yourself a new email address, try to recall what personal details you have given these people when you contacted them. Change things like phone numbers if possible.
Rule 3 - search for your details online, see if your email address is posted somewhere public. If so, remove it. Even on places like Friends Reunited, your email should not be visible to everyone.
Rule 4 - stop forwarding those "send this joke to ten people you know" and "If you send this to all your friends you will have good luck" emails. They are a device used for harvesting email addresses, that's all they ever are. There are no little girls dying of some awful disease who will ever get better by your sending someone an email. If you want to help people, give a fiver to your local hospital!
Rule 5, have fun.