House Undervalued- what options do i have?

hello,

I am currently in the process of remortgaging from halifax to santander.

When halifax sent over their retention offer they valued my house at £370,000.

I used the figure they gave me to get a decision in principle to santander.

after passing the credit checks and affordability santander sent over a chartered surveyor last week. today i'm told that they value the house is £350,000. i think that is fair enough as i did think the halifax valuation might be a bit on the steep side.

Valuing the house at this amount puts me at 62% LTV. The product I wanted and applied for was at 60% LTV. I have savings and have offered to overpay the difference with halifax so that I borrow less from santander and make the LTV 60%. i originally asked for £214K, to get to 60% LTV would be £210k

In peoples experience are santander likely to accept this, or might they withdraw the offer?

I'm a bit worried as the product is no longer available and the current deals i have researched aren't as competitive.

santander tell me they have a back log atm and will take a week or so to get back to me. so in the meantime i wanted to ask you folks if you have any knowledge of what is likely to happen next.

any opinion would be greatly received : )