Of course it can be done, it isn't rocket science.
Small but significant changes are the key. Choose better meal options, if you are living off frozen pizza and takeaways then you need to swap to better options. Consider some chicken with a bit of veg? Don't jump in and try to manage on tiny portions or missing meals, that is a sure way to fail. Cut out continual snacking between meals, this can make a big difference. Just as a small anecdote, I was recently waiting outside a supermarket and spotted 4 girls/young women returning to a car having done some lunchtime shopping. One of the girls was noticeably big in an unhealthy way and as they were loading their shopping bags into the car boot the large girl was stuffing food into her mouth! Like I said, it isn't rocket science and medical issues aside a lot of the required changes can be obvious when viewed from the outside.
Now something I have said many, many times in response to posts like yours. Use your bike for everything. Don't get into the whole 'today I will go for a bike ride' mentality because it won't work and those rides won't happen. Instead, just take the bike for every errand. Nipping to the shop for some milk, hop on the bike. Getting money from the cash machine, ride to work (if it is a doable distance), going to the pub, visiting family, anything. Just use your bike and you will be amazed at how the short trips add up to a significant distance and big change in fitness. No big change in the things you do, just doing them differently. My car can often remain unused for nearly a week at a time and I live 10 miles away from work. Try it, you will like it and the smug feeling of breaking free from the system is very satisfying.
Anyway, enough waffling from me, the weather is nice in Manchester today. Don't know exactly where you are in the northwest but today is a good day for a short ride out......
