Living in the UK growing mangoes outdoors isn't possible as the winter frost would kill them but they can be germinated and grown in pots and moved outside during the summer months as patio plants.
Growing from seed means that the plant is a juvenile so would be unlikely to fruit for a decade and you would need to graft onto a mature rootstock if you are looking for quicker timelines.
For this example I've used Alphonso mangoes which a re a small sweet orange fleshed variety popular in India but this will work for other varieties and even avocados.
After eating the mangoes clean off the left over flesh. I found the best way was to use a scouring pad under the tap. Leave to dry on some paper towel for a week.
Once dried the next stage is to remove the outer hard shell to expose the inner seeds. This is a tough job and I used scissors and garden secateurs to snip at the outer edge. Take it slowly and carefully and try not to damage the soft inner seed.
The inner seed is then placed on some paper towel and layered with as many seeds as you which to grow - in this case 3 seeds each on 2 pieces of towel. This is then put into a zip lock bag and the towel made damp. The bag is then put into a warm dark place preferably above 25C - I put it on the hot water pipes coming out of the heating boiler.
This is then checked once a week to change the paper towel if it is stained or mouldy or topped up with water if it's dried out. Germination can be between 2 and 6 weeks.
See Part 2 for germination and potting.