Hiya,
There are a couple of things can cause this.
First, ensure the machine has emptied all the water.
I'm assuming the handle and latch assembly isn't broken, you would know because the assembly would be loose and floppy.
If not empty, put it on a spin programme again and see if it empties and unlocks.
If it's empty and won't unlock, unplug the appliance from the wall socket and try the door again after 5 or 10 minutes.
If it still won't open then the door lock has gone faulty and jammed in the locked position.
This is a bimetal strip within the lock and it's sometimes possible to shock it loose.
On the side where it locks give the door a good hard thump, see if this unlocks it.
If it doesn't unlock after 2 or 3 thumps it's not going to unlock.
Take the top off the machine and reach down the front till you find the door lock.
"Jiggle" the lock around a bit in the hope it will unlock.
If after all this it persists in staying locked you will have to work the lock back and forth, side to side until it comes off it's screws.
You should then be able to lift the lock off the latch and the door will open.
You would then have to replace the lock with a new one.
Alternatively, get some nylon cord, feed it into the door recess and work it round till you have both ends opposite the door handle.
A few good tugs on the cord until you break the door latch off will enable you to get the door open.
In this instance you'll need a new door lock and handle/latch assembly.
Good luck with it.
Hope this helps
Let me know how it goes or if you need more help.
Thanks
Home Appliance Technician
Whitegoods engineer working for a multibranded national company in the UK.