Well I'm happy to say I've done the first day and I feel a wonderful sense of achievement.
It wasn't easy but for anyone attempting this, here's what helped me:
Chatting to people who've been through this already on this forum.
Getting lots of support.
Eating whatever I fancied, and being told not to worry about food since I can tackle that problem later.
Making a list of tasks to keep myself completely occupied for the whole day.
Avoiding situations where I normally would have had a cigarette.
And I do realise that all of the above isn't possible every single day but I've set myself a target of 21 days because I heard that's how long the brain takes to make or break a habit. I'm taking this one day at a time.
I downloaded an app that tells me how my health is improving by the hour which to me is a huge help as I have so much health anxiety especially about the effects of smoking. (Yes I know, makes you wonder why I ever smoked if I have such a fear, but we all happily ignore the warnings on the packs)