Here is a part of an email I received on 20 March from Barclaycard:
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Dear Mr Ellipsis
I’m writing today as I know that coronavirus is a source of concern for many people right now – and I wanted to let you know we’re here to help.
Whether you would like additional support with managing your Barclaycard, or have faced disruption to finances or travel plans, we can work with you to look at ways to make things easier. To help with this, we will be stopping late payment and cash advance fees for Barclaycard customers for the next 90 days – we’ll take care of this, so you won’t need to call us.
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"stopping late payment and cash advance fees for Barclaycard customers for the next 90 days" ... this is good. I would require M&S to do likewise, when you can get through to them. You can see why Barclaycard have done it, with so many flights and concerts being cancelled that have all been paid in advance. It saves them a lot of admin to just let you take the cash back out (and if you take out more than you're in credit, you start paying interest on the extra).
If you were really desperate for the cash then I would withdraw it and, if they subsequently charge you a cash advance fee, argue the toss with them about it and if you're ultimately unhappy cancel them and get a different credit card.