Although I will not turn down cash donations it is preferable to donate via BT MyDonate page here.
“MyDonate doesn’t charge any commission fee, subscription fee or registration fee. The only fee taken from your donation is the charge for using your card. This fee is raised against the total donation value and paid by the charity when we make payment to them. The fees are 15p for a donation made using a Debit card and 1.3% for a donation made using a Credit card. Where a donation is being made to more than one charity, the fee is split between them“.
If you would like to donate using cash that’s fine. I will make a note of the amount and whether you are donating to the three or only one of the charities.