@CorianderLord
As you have cancer you are technically covered by the Disability Discrimination Act - this means it is illegal to fire you for some thing pertaining to your sickness (like sick leave). It covers you when in remission also
All of that is wrong. The DDA is no longer applicable and hasn't been for ten years. And it is certainly not "illegal" to fire someone for something pertaining to an illness, whether it is a disability or not.
An employer is obliged to make reasonable adjustments to enable a disabled person to return to work following illness/stay in their job or in an alternative job. They are not obliged to keep someone employed indefinitely where they can't do their job, or where there is no alternative job, or reasonable adjustments available.
The time when it may become reasonable for your employer to terminate your employment will depend on a number of factors, including their capacity to make adjustments, or to redeploy you or sustain your absence. This period is usually longer in a bigger business for obvious reasons - they usually have more capacity to manage with longer term absence, or cover it, or afford more expensive adjustments, or redeploy to other jobs.
I agree with Bluntness about the anxiety being an issue, but if you're involved with occupational health that's good, and being recommended a phased return. If you do go off again then there's no point pretending there's not a risk you'll end up out of work, so use that to motivate you to get some help with your anxiety as well as your physical condition. If your OH feels you can cope with a phased return that's really positive.