How much borrowing?

Hi all,

We are looking into the options of borrowing additional money.

Basic outline, house owned worth £950,000 with a £350,000 mortgage. Looking to borrow an additional £450000 to purchase a second house for £450,000. Is it possible to joint the houses together to give an asset value of £1,400,000 thus making the LTV of 58% for the £800,000 borrowing.

Is it possible to borrow this Interest only?

Is it possible on a joint income of £85,000, based on such a large amount of equity?

Thanks for any help.
Phil