If I want to sell my house, how about my outstanding mortgage ?

I am thinking of buying a house, however, I am not sure if I would stay here for good. Let us say, I bought one house with market value of £100,000, paid £15,000 deposit and get mortgage from the bank for the next 25 years. If I decide to sell my house after two years, what should I do with my... show more I am thinking of buying a house, however, I am not sure if I would stay here for good.

Let us say, I bought one house with market value of £100,000, paid £15,000 deposit and get mortgage from the bank for the next 25 years.

If I decide to sell my house after two years, what should I do with my outstanding mortgage. Can I transfer it to buyer? I heard that the estate agency and solicitor will get involved in this matter, what kind of roles do they play?

I will appreciate if anyone can explain to me how it works in details.
Update: Thanks, guys. Another question just got into my mind as reading your answers. By the time I sell my property, I do not think I am able to pay off the outstanding mortgage. And the buyer may have to get a mortgage from bank as well. Does that mean I could not sell my house until I own it completely. show more Thanks, guys.

Another question just got into my mind as reading your answers.

By the time I sell my property, I do not think I am able to pay off the outstanding mortgage. And the buyer may have to get a mortgage from bank as well.

Does that mean I could not sell my house until I own it completely.
Update 2: Sorry, I forget to add. The new property I will get will be abroad.
Update 3: Quoted from twinkle: "When you sell the property you repay the outstanding mortgage from the proceeds from the sale. For example, you sell your house for £125,000 when you still have a mortgage of £80,000. You repay the oustanding £80,000 to the lender and you keep the remaining £45,000 (from which you pay... show more Quoted from twinkle:

"When you sell the property you repay the outstanding mortgage from the proceeds from the sale. For example, you sell your house for £125,000 when you still have a mortgage of £80,000. You repay the oustanding £80,000 to the lender and you keep the remaining £45,000 (from which you pay estate agents and solicitor fees)".

My confusion is that it is unlikely for the buyer to offer £125,000 cash, how am I going to pay back the outstanding debt.
According to other answers, my understanding is that the buyer will take a mortage to cover mine. Am I right?
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