Hello,

This is nothing to worry about! What you need to do is put the car in
1st gear and try and pull away (as you say make the rear dip), then
switch to reverse gear make the front of the car dip.

Just keep doing this back and forth until you hear an almighty bang
sound. That's the sound of the brakes releasing. They've seized by the
sounds of things.

Start gently but as you go back and forth put a bit more pedal on if
needed.

Once it's released obviously check the hand brake's correct operation!
And foot brake too. But it should be fine.

If you want to be extra cautious pop the car to your local garage and
get them to check the cables, and brakes. I did this the last 2 times
when my car had this prob and each time the garage said nothing wrong
(I have an honest garage that won't do work for the £ of it).

Good luck, John