It's difficult to put numbers to your individual situation - too many local and personal variables. But you can do your own spreadsheet. On £16k you'll bring home about £1200 per month. Your rent looks to take half. So £600 per month to cover council tax, electricity, gas, water, food, clothes, phone, Internet, entertainment and car costs. I expect I've missed some key items there - but each item is quantifiable with a mix of Internet research and real life shopping. So make a list and try to get a sensible figure for each item. Car costs can be a big deal - especially insurance and lease payments. Make sure you separate essential costs which have to be covered and discretionary which can be trimmed.
You'll need some capital up front, because most property rental needs a month rent in deposit, plus first month paid in advance.
But best guess is that in lower cost parts of the country it's doable with care, and you've got the yearly increase to look forward to.
Adding your girlfriend's £11k to the deal makes it much easier - many costs - rent etc - are no more for 2 than for 1.