Does lender valuation protect me from high offer?

All the lender is concerned with is that they have a reasonable chance of getting back what they lend if you fail to pay.

To get a realistic price, look at recent sales of similar properties on that street or nearby.

Sale prices are on public record and you can view them on the land registry web site - see the link below & enter the postcode of the house.

Try other nearby postcodes as well, or just vary the last character up & down for nearby streets if you don't know them.

http://houseprices.landregistry.gov.uk/

The lender valuation is to more to protect the lender not the borrower, this is so the lender does not lend more than the value of the property so if a borrower defaults they should be able to recoup their money, although when markets fall this still happens. Although you should get a valuation before putting in a sealed bid so you can base you bid on the valuation amount.

for e.g. If you put a sealed bid of £300K, the valuation comes back as £280K the lender if approved the loan of £250K should still give the loan as their part of the property is still over 250K it is up to you then to deciced if you still want to offer the full amount. (this is just for example i know nothing about the value of the property you are taking about)

in a seal bid sale each sealed bid may have their own lenders valuations.

All I can tell you is my experience. On Friday, contracts were exchanged on my house. The couple who bought it offered 70K over the asking price. They had a mortgage valuation done and a survey. Every moment I expected the offer to be lowered. It wasn't. Their mortgage company approved their loan amount. My house sold for a lot more than similar properties on the street and although it was mine, I know there was nothing really special about it.