I have just completed a job that required the use of *Wickes Matt paint in two colours. One colour (Scarlet) was of a good consistency, the other (Cardamon) was so thick that the tin could be completely upturned without any paint falling out.
This is of course the wrong consistency for wall paint and attempting to use paint at that thickness would result in twice the amount of paint being required to complete the job, as thick paint doesn’t go very far.
So a rescue job is what is called for. Scoop about a third of the paint gloop into a separate container or bucket and add an equal amount of water. Mix thoroughly. You will now have paint of a good consistency and can get on with the job.
Whatever you do, DO NOT tip the whole tin of paint into a bucket and add a load of water to thin it – the chance of getting the proportions wrong and ending up with an unusable tinted water mixture is high. Do it little by little.
*Wickes do produce good quality paint with strong pigments but the consistency of their emulsions is variable.