I don't know where you are in the UK, but in all but the warmest regions, Gerbera are treated as half hardy annuals. They will need heat when you first start growing them, 68 to 72 deg F, and like high humidity, and will need to be kept in a frost free environment if you want to be sure of having flowers. Also bear in mind these plants usually don't flower prolifically in their first year, producing many more flowers in their second and subsequent years, if they survive that long.
If you google 'red gerbera seeds' you should find an online supplier - decide on whether you want double or single flowered forms.

By growing yourself you also have no guarantee that there will be flowers for the wedding day... So, you can try but be aware that it might not work!

Keep the florist's number handy!

I would pre order from a florist (Market stall) for quality flowers to guarantee for a specific day. That way you can get uniformity of shade and size as well.

They do advertise "Hardy Gerbera" down to -5 but I seriously doubt that they are.

Me too Pimpernel!

I grow lots of perennial gerberas here and they all survived the minus 12 temps of last winter, they grow in the ground in my front garden.

I was about to add that Louise, in the west country, has these as perennials in her own garden, so glad you did, Louise. They just die over winter here in London.

Rose has put up another post thanking us all and saying she has decided against