Thanks Freddy, the cartridge retaining top clip had sprung up and I managed to slide a thin steel rule over it to hold it down while I pulled the carriage assembly out (it was jammed by the aforementioned until) and install the ink.
I mend all sorts of things up to and including Combine harvesters but always better to ask before damaging delicate stuff like this. I bought this new and another previously off Amazon for about £18 some time ago but they're not there now, so pleased its working again, Cheers!
.I am glad to hear it's working again please don't forget to leave a positive rating it is greatly appreciated.
I also suggest keeping an eye on the carriage assembly, the strip behind it could cause this. If it does just make sure to clean the strip as best you can with a lint free cloth.