Yogi, it's always hard to watch someone you love suffering and declining. One of the most important things for you is to maintain your equilibrium by not taking everything on yourself. You and your mom need, and can get, help.
In America, many elderly people with health problems can still live in their homes with help from organizations known here as the Visiting Nurse Service or its equivalent (churches and other religious institutions also provide this kind of service). Our government-run health agencies, Medicare and Medicaid, can provide in-home assistance or other help. And many private agencies provide companions and home-health aides, too.
The reason I mention this is because I'm sure that the UK has all of these types of options, and probably more, since your health care system is more "socialized" than ours. Once you start the ball rolling, you'll start feeling that you're not taking the entire burden on your shoulders. And remember: you're not stopping your care and love for your mom--you're getting her the professional help she needs, which can free you to provide the emotional support and love that only you can give.