Does having a larger deposit effect the chances or actually getting a mortgage or does it effect the amount they will give you?
Don't think anyone actually answered your question.
In case you've not already had a read up on it. A larger deposit doesn't necessarily mean you'll have a better chance of getting a mortgage, i.e. you could have a 50% deposit, but with a very bad credit rating, the lender might not be willing to trust you.
The amount they lend you should only be based on your income/outgoings rather than taking the deposit size into account.
What the deposit size will dictate is the interest rate of the mortgage. As a minimum you need a 5% deposit, which would be a 95% LTV mortgage - the rates on these are quite poor. It then sort of goes down in bands, so 80-95% LTV you might see a 0.2% drop in rates. Then 60-80% you might see a further 0.2% drop.
Typically though, the bigger your deposit, the better rate of interest you'll get.