If you are starting out with acrylics or watercolours there may be a few paints that you want to add later on. In addition, if you are going on the Borde Hill trip in June there may be a few essential colours that would make all the difference.
Main core set of colours that are necessary: blue, yellow, red and white (for acrylics). However, you might like to take a look at the paint names and if you are online or in the shop, make a note of all the other colours, say a blue that you can also choose.
More advanced set of colours would be: 2 blues, 2 yellows, 2 reds and a white.
Then you might like some special colours: a bright pink, a great purple and some of the earth colours: burnt umber, burnt Sienna, Yellow Ochre and black (Borde Hill recommended)
Buy what you can afford and if it is just one great pink then super! Keep the lids on the acrylic paints (get them off under boiling water if they stick).
The Range in West Worthing is a good local source, Hobbycraft in Angmering or further are Lawrences Art shop in Hove and the new Cass Art in Brighton. Happy shopping