I have two full fare J class singles booked from MLE to Gatwick for 3 May and want to be able to cancel and rebook if earlier and/or cheaper availability opens up. However, when I try to cancel the originbal booking, the option is greyed out and if I click on it I get the message "We regret that due to the nature of your booking we are currently unable to make changes on ba.com". Any idea why this should be?