Yes & no
Money held in a joint accoint is deemed owned 50/50. So if you have seperate accounts and 50/50 in each account then you will be in exactly the same situation.
Have all your money in the account of the deceased and then you will have more trouble and more tax.
What sometimes happens with joing accounts is that one neglects to tell the bank the other party ahas died nd takes all the money and leaves the account dormant.
For foreign people it is a real nuisance if the only Spanish asset on death is a bank account because you will need to present certain documents to the bank to get access to funds (a probate of sorts) unless again you neglenct to tell them and somehow withdraw all the money.
Many people know they are on the way out and for foreign people that is an ideal time to sort Spanish matters out and excape Spanish inheritance tax particularly if there is not IHT in UK.
I'm not saying any/all of above is legal but it is tax we are trying to avoid so all is fair!