I downgraded, credit limit stays the same (I asked) and interestingly if/when I decide to go back to the premium card then 241 spend will transfer to the Premium card i.e. if I spend £14k on the basic card, as soon as I upgrade I will receive a 241 voucher immediately… Also called Amex Platinum with a view to cancelling and they are actually offering an incentive in the form of Rewards. I may still cancel if the lockdown looks like it will continue (I will review July/August when hopefully we will know more about SARS-CoV-2) and the 2 Avios per/£1 spend is a good deal... I should add that customer service with AMEX is invariably excellent...