Can we get a mortgage?? Need advice to help us make our mind up!

Homebirds

Thank you very much for your advice; it's really helpful. We are going to use the cash for the improvements; I totally take your point about one income bearing everything so I agree it would be sensible to use my partner's income, too. And paying off the debt is certainly a good idea too.
The mortgage we have is portable which is very useful; we may approach Nationwide again to see if there's any way forward but will also contact an IFA tomorrow and arrange a consultation.
Thanks to you all for taking the time to respond, much appreciated.