First Direct Mortage Advisor says mortgage affordable but their underwriter says no

stella1w

Long term, more than 25 yrs, First Direct customer. All products with them, good credit history, good job, tons of equity in house, seeking additional borrowing for loft extension which will add value to property.
Go through application with their mortgage adviser who says I I meet affordability.
However, their underwriter says no due to high childcare costs. Mortgage adviser said the borrowing was affordable even with these costs. Plus they will halve in sept, date of drawdown, when youngest starts school.
Underwriter wants evidence. I can provide payslips to show what I am currently paying my carer eg. Her rate of pay and a letter confirming her reduced hours from sept. But it seems underwriter wants track record evidence eg three months of the lower payments which I wouldn't have till December by which time the current good rates might have gone esp post Brexit and the loft extension would be delayed by a year.
Any advice appreciated.

minimike2

First Direct = HSBC = Most stringent lender out there.

You aren't likely to have an easy time with this.