Borrow on one property to spend on another

demontfort

Hello,
My 2 year fix is coming to an end in November and I'm looking to remortgage with a different lender and borrow an extra £50k at the same time.

• The property that I need to remortgage is worth £380k with £22k left on the mortgage.
• I own a second property also on a residential mortgage with my partner which I plan to spend the £50k on improving. Mortgage is £270k on a £400k property.
• Both mortgages are residential and neither property is rented out nor will they be rented out in future.

I'd appreciate any comments on the below:

1. Would 2 residential mortgages throw up any red flags for increased borrowing?
2. Is it worth the hassle of switching lenders if I want to borrow more? I would save about £350 (25bps annually) in total over a 2 year fix period by switching. 
3. If I switch lenders, will I be able to borrow the extra £50k straightaway? I'm considering moving to Nationwide or HSBC, current lender is First Direct.
4. What evidence would they need to see regarding the renovations? I have planning permission but would they need builders quotes?

Many Thanks,
J