Outrage over shops already rejecting old fivers

Can a shop reject your old paper fiver before it ceases to be legal tender at midnight tonight?
I just heard from an irate shopper who had been given an old fiver as change in a supermarket, then had it rejected in a coffee shop and then rejected again in an organic grocer's.
It looks like there are a few cases of traders not wanting the hassle of dealing with defunct £5 notes now they're on the way out.

Can a traders reject your old fiver already?

The answer is yes! It's up to the shop what they can accept.
They can reject £50 notes if they don't like the look of them.
Equally, they can accept magic beans for currency if they want, or chocolates, or gig tickets - whatever you agree with them.
The acceptability of notes is entirely between the two people involved in the transaction.

So what's the point of saying it's no longer legal tender?

Legal tender is a tricky concept. It means that the money being offered is good for paying a debt.
Someone to whom you owed money could reject magic beans as a payment, but not legal tender.
And a court would back you if you paid with legal tender.
Tonight the old Elizabeth Fry fiver stops having that unassailable legal status.

The Bank of England says, “It means that if you are in debt to someone then you can’t be sued for non-payment if you offer full payment of your debts in legal tender.” Here's the Bank's brief.

Can stores carry on accepting old £5 notes if they want to?

They certainly can.
Any supermarket, High Street shop or market stall can take an old note from you next week and for the forseeable future, if they are feeling nice.
First of all, it's up to them what they accept.
Second, they are likely to be able to deposit an outdated paper fiver at their bank for months, if not longer.
And the Bank of England will accept old fivers "for all time". Here's how you take them back.