Can I clarify - there is no loan from the govt available or offered for those using the new Help To Buy Mortgage Guarantee scheme to buy a non new-build. For those wanting to use the new scheme to buy a non- new-build, they will need to apply for - and have earnings high enough to get - a 95% mortgage, same as now. There seems to be some confusion on this thread with the earlier Help to Buy Equity Loan scheme (for those buying new builds ONLY) which offered a 20% equity loan from the govt, which started costing lots of interest on top of the mortgage, if not paid back within 5 years - clearly a bad idea.
The mortgage guarantee scheme is not really as revolutionary as it is being made out to be - the only difference to now is that the govt will guarantee the lender that if prices fall and your property is repossessed, they ie the taxpayer will pay the lender the next 15% of the value of the property - on top of your 5% that the lender has taken too. So the govt guarantee is not to protect the buyer, it is to protect the lender.
The only supposed benefit for would-be buyers as a result of this guarantee, is that banks are supposedly going to offer 95% mortgages at better rates than they do now, when all the good rates go to buyers with large deposits of their own. But 95% mortgages are already available and the rates on the open market don't sound very different from those mooted as likely under the new scheme eg the Telegraph suggests rates of 4.5-5% for a 2 year fix, which is worse than you can get currently anyway.
So suspect the scheme will actually make very little difference to first time buyers, whose problem is that house prices are just FAR TOO HIGH. They would be foolish to take out a 95% mortgage on a 2 year fix when rates are at historic lows and about to rise, unless they are sure their earnings are likely to rise soon too considerably to keep up with the costs once interest rates shoot up.
The govt has introduced this prior to the election to try to ramp up prices and bring on a housing inspired boom to present the image of a growing economy - just in time for it all to crash the second the election is out the way.