This is obviously a scam and you will be asked for money at some point. At that point you may feel that you are so close to coming to the UK that you may well pay up as many others before you have done, especially when they tell you that this money will be re-imbursed once you get to the UK
As Darren says, the UK will not issue a visa for the kind of jobs you describe. Even nurses can't get visas these days unless they are highly experienced and specialist in some way. Caregivers are no longer given visas either. The only visas issued for work purposes are for highly skilled jobs for which there is a shortage of suitable applicants in the UK and these particular kinds of jobs are on a list provided by the British government. If you ever do recieve a genuine working visa, it will be fixed inside your passport, it does not arrive in the form of a letter. The British Embassy doesn't even inform you if your visa application has been successful, they merely return your application pack with the visa slip fixed in your passport, or a letter explaining why you have been refused a visa and details of your right of appeal.
Iain.