I wish you a successful experiment, that can maybe last beyond the month.
If you are doing it for health reason, I would like to add a personal suggestion to embrace the VEG part in VEGan and avoid all the Frankenstein-food such as vegan sausage, vegan burger, vegan cheese, vegan bacon.... they are heavily processed and from a health point of view , far worse than the animal version.
Learn how to make falafel, veggie or mushroom based burger , discover the versatility of chickpeas, explore tempeh, rice paper wraps and so on.
The second recipe I gave you is a good substitute for minced meat in all its use, so great for Mexican.
I hope you will find veggies in the supermarket, it is a crazy situation you are now facing in the UK. If only weird veggies are left, use that as an opportunity to explore new vegetables. People tend to only eat the same 6 veggies over and over.
Ed Smith has made a wonderful book called On the side, it is not a vegan book, plenty of butter listed as ingredients, but just change it for Extra virgin olive oil, but of all the cookbook I looked at and bought it has the biggest variety.
Middle Eastern cookbook are also a good source of inspiration.
Make it a challenge to try something new at least 3 times a week (out of the 14 meals you will have in a week).
I discovered a new way of cooking and some dishes you will like, other you won't. The New York Times has many recipes such as cooking.nytimes.com/recipes/1016062-red-lentil-soup-with-lemon
Consider also quinoa. I cook mine with 1 cup quinoa for 2 cups of water, and will keep a container in the fridge. Look for black rice as well.
You might want to start buying vegan essentials now if you can, so nutritional yeast ( a must for cheese substitute : vegan parmesan= 1 cup of cashew, 2 heaped tbls of nutritional yeast, 1 tsp onion powder , 1/4 tsp salt , blitz in blender. ) Note , if you have a lot of it, your pee will be bright yellow because of the high vitamin Bs content.
Good quality extra virgin olive oil, soy sauce, if you can find it liquid smoke, cherry vinegar, a ton of lemons, chickpeas, even dry, edamame . good quality passata (Mutti is expensive but worth every penny) , a variety of seeds to make seeds crackers.