what caused all elements to shortcuit on hotpoint ew81 electric cooker?

Your description "all elements to short circuit" simply doesn't make sense as you immediately go on to tell us that some elements (the top hob) work OK. Please make your mind up.

Is it connected to a proper cooker circuit?

Is the "trip" an overload (Cooker trip opening) or is the earth leakage protector tripping?

If yu are confident that it has been installed correctly and you didn't get a monkey with a screwdriver to do the job on the cheap, I am inclined to agree with the other suggestion: get the thing looked at under warranty.

If you didn't get a professional (or at the very least someone who knows what they are doing) to install it, GET THE INSTALLATION CHECKED BY AN ELECTRICIAN BEFORE YOU KILL SOMEONE YOU CARE ABOUT

Me here wearing rubber gloves
October 2015

warranty problem. Get the retailer to sort it

Read up on his responsibilities under the sale of goods act 1979 (as amended)

xxx
October 2015