It’s best to be in continuous work for at least 12 months before you get a mortgage, but not essential. Some lenders offer mortgages to people who have been employed for less time, say 3-6 months, and it’s even possible to get a mortgage while you’re in your probationary period, but this is often not advised as you can’t be certain of your income and ability to make long-term repayments.
To prove you can make the repayments you usually need at least 3 months’ payslips to evidence your income, this is why it’s best to be employed for at least 3-6 months before applying for a mortgage.
Different lenders offer different deals, but if you’re able to prove you can make repayments and keep a consistent income, you should be able to get a mortgage.