To be honest I don't know the answer to the problem as I gave up selling on eBay when Managed Payments came in, but I've been trying to think of some workaround solutions to the problem that you could try out.
If you can't get around the problem at the moment try logging off of eBay UK and log onto another eBay site, such as www.ebay.com, which is the USA version of the site. If it's a glitch specifically affecting eBay UK then by logging onto an overseas eBay website you may be able to edit the postage label.
If the above suggestion works then when you get back online and you click on the Edit button try looking at the address to see whether there is anything that could be edited down to reduce the overall character count. For example, if the buyer has put 69 Saint George's Avenue as the first line of his/her address, abbreviate it to 69 St George's Ave, and if the name of the county has been stated in full and is rather long, such as Gloucestershire, chop it down to the abbreviated version and put Glos.
If there are any instances in the address where this theory could be applied try it out and see whether it brings the total character count back within the maximum permitted amount of characters. If it does then the address label ought to print off, and abbreviating certain words as I described wouldn't cause the Post Office any problems with regards to ascertaining where to deliver the parcel to.
In the event that this suggestion doesn't work, then the next best workaround option would be to give up on trying to print off an eBay postage label and just write the buyer's postal address out in full on the front of the parcel so that it matches exactly the address provided at Checkout, ensuring that you also include a returns address on the back of the parcel, just in case the parcel cannot be delivered for some reason. Once you've done that go down to the Post Office and buy a postage label there, then enter the tracking number as soon as possible once you get back from the Post Office.
