Getting a valuation for a better deal?

trev2020

We purchased our house almost 5 years ago and took out a 5 year fixed rate mortgage deal. We have two months left on our current fixed rate deal. During the last 5 years we've had added an extension to the property and made numerous other home improvements. In addition to this two similar properties on our street have recently sold for roughly £70k more than what we paid back in 2015. Our current mortgage lender have offered a new 5yr fix rate deal based on the valuation from 2015. There offer is based on a 75% LTV, however, if we go with valuation of based on the sell price of the two mentioned properties we'd come out with a 65% LTV rate. 

How do we go about getting a new valuation, an estate agent i presume? I guess they'll charge for providing a written evaluation service as we've no intention of selling the property.  I've shopped about various mortgage lenders/compare sites and there a significant saving to be made, especially if we can land a 65%.

Any tips or advise would be appreciated.

RelievedSheff

Remortgage to a different lender who will do a valuation on the property as part of the remortgage process.

Thrugelmir

Does your existing lender offer any products with an LTV between 60% and 75%. Little point in paying for a valuation for no benefit.