OP, with 20% you should be able to find some respectable mortgage deals out there as I am sure you have probably seen.
Bare in mind that if you are getting to near 25% you will need to factor in other costs such as solicitor fees, moving costs, new furniture, having some savings spare for when you have moved in, possible stamp duty if it lowers soon it's being suggested, etc.
My house was just under stamp duty and we had a 85% LTV. We had more saved and could have probably stretched to 20% but considering EVERYTHING else we would have sold ourselves short and realistically needed another 3-6 months worth of savings to be comfortable.
Having said that, the process of finding/buying takes a long time and we offered around August and are completing a week Friday. We took our time and just let the process run it's course because we were saving the whole time
What is your credit rating like? Are you in any debt (bar student loan) with credit cards etc? Did you achieve the 15-20% you have now on your own or was it a gift from family? Do you pay into a pension scheme?
Questions like the above will inevitably determine if banks are interested. Generally if you aren't in debt and have a nice chunk of deposit and good credit rating they will have no problems in lending you the money. Although as first time buyers the deals are never really that sweet unless you are putting down huge amounts of money on a deposit.
To add to what CM1179 and Showboat said above, they recommend that roughly 1/3 of your total monthly income should cover a mortgage payment. Leaving the rest for " enjoying life" (I.E - Bills, Food, Saving, Etc). This should also leave you in good stead for planning for things like interest rate rises.
It then depends if you want to mortgage over say 35 years, if you want a fixed 2-3-4-5 year deal. Protection from interest rates rising until you come out of that term but slightly more on the monthly payments. If you think you'll be earning more in 4/5 years then it might tie in nicely.
It's all a lot of ifs/buts and whats suited best to your position at the end of it all. No one knows what is going to happen, the benefit of hindsight, if only we could have it now.
The main thing is if you are moving with the intent on buying a home or an investment to make money from, if it's the first then that is a better term to be considering buying at the moment, imo
