We have had several customers notify us that they've having connectivity issues in the Cambridge area, all FTTC customers so far, where TCP packets larger than 1300 bytes appear to be dropped. ICMP appears unaffected.
We are currently in the process of reporting this to BT and will post further updates as they become available.
Proactive have raised a fault, AF-AR-OP-3774655 This has also been discovered to affect FTTP customers, which makes sense as they use the same backbone infrastructure as the FTTC customers.
Several customers are reporting that their lines are now performing as expected after restarting their PPP session, so it may be worth restarting your PPP session and letting us know what happens when you try that.
We're still awaiting an update from proactive.
We have been advised by BT that a link between Milton Keynes and Peterborough was erroring, and was taken out of service to resolve the issue earlier today.