Hi Laura,
I am a resident of Gloucester so understanding your situation very well, I've just worked out how to get the lid of my dual flush loo so thought I'd let you know asap.
I'm hoping you have a short flush & long flush button like me, what you need to do is push down one of the buttons & hold it, whilst holding it down have a look at the other button now that the side has been revealed, on mine it shows arrows pointing up & the words service, I then worked out that you simply pull the button upwards, once one half is out you can lift the other out as well, remove the chrome ring and underneath where the buttons were was a screw that I used a knife to turn, once this is unscrewed the top just lifts off.
I really hope that your loo is the same sort of design & this works for you, let me know how you get on.
Good Luck :-)
Deborah Ferris
July 2007