I would urge you to look into and really understand the information in the post by @TimetoGetUpNow
Mortgage interest is not treated as a deductible expense but you are given a 20% credit against the mortgage interest.
If you are a higher rate tax payer or the total rents you receive make you a higher rate tax payer your tax will include 20% on the mortgage interest you pay. The reality of this can mean landlords having a tax bill on a loss.
The capital repayment part of your mortgage is never deductible and tax will be due on it.
People who think they have no tax to declare because they are charging 1k each month and their (repayment) mortgage is 1k each month are entirely wrong.
Another effect of this is that your income from property (without deducting mortgage interest) is shown on your tax return and makes your income look higher than it actually is (as you have had to pay the mortgage interest).
If your kids go to uni the help they get for living (not fees) will be means tested based on your household income. Your household income will appear as all your rent receipts less your maintenance expenses /insurance/agent costs etc. Your mortgage interest will not be deducted from this income. E.g. if you receive 15k of rent in a year and have 3k of expenses disregarded then this will add 12k to your household income and as such reduce the help your children can receive at uni - while it is actually difficult for you to lay your hands on any of that cash because most of it has gone into your mortgage.
If you are a lower rate tax payer - and will still be a lower rate tax payer when receiving rent, if your kids aren't going to uni or won't get means tested help anyway (kind of conflicts with first point) and if you can afford to pay your own rent even if your tenants don't pay theirs it's not too bad an idea.
If you go ahead please at least use a tenant finding service - I would also say a managing agent. Choose tenants that can afford to pay their rent and have good credit and references unless again you can afford it when they don't pay or damage the property.