As Rileyroo has said, McMillan have some good advice on their website, they may also have a benefits advisor in your area. Mine was able to fast track my Personal Independence Payment application by dealing with the DWP on my behalf (which saved me a lot of hassle whilst I was coping with chemo side effects). PIP is not means tested so you will get it whether or not you are employed and regardless of how much money you have. PIP makes you eligible for free prescriptions and for a blue badge for disabled parking but once you're receiving PIP you need to apply separately for these.. There are other benefits which you might claim but some of these are means tested.
If you are currently employed you will be able to claim some sort of sick pay while you are off work - at the very least Statutory Sick Pay. Talk to your HR Department and your Trade Union (if you have one) - don't just resign or you may lose out big time.
