Answer - Part 2
There is nothing to stop you taking out a second mortgage now, to cover the short-fall, but without knowing the likely short-fall; how much you need to pay and for how long, cannot be determined.
Check out this site to work out monthly payments required on a mortgage – you can enter/change the mortgage amount (loan), and length of mortgage, to see how these affect the monthly payments.
http://www.fsa.gov.uk/tables
If you don’t get another mortgage (or don’t want to), you could sell and downsize or relocate to a property which you could buy outright with the proceeds of your house sale.
My advice is to take advice from more than one mortgage advisor – there is nothing stopping you from applying directly to one of the providers, shown in the fsa tables.