All florist's shops are closed to walk-in customers, including those used by services such as Interflora for delivering orders taken by phone or online. A
fewremain able to deliver online orders but
(a) most shops won't bother if online orders only form a very small part of their business, as it won't be worth ordering in stock ; and
(b) to enable florists carrying much less stock than usual to accept online orders, Interflora customers have to accept the bouquets and arrangements that the florists choose to provide. (i.e. other than price, you don't get any choice as to what's actually delivered).
Interflora's website includes a link to a postcode checker from this page:
https://www.interflora.co.uk/blog/coronavirus-update/
(It's at the top of the page you get to. Remember to enter the recipient's postcode, not your own!)
That will show your whether there's any delivery service available in the relevant area. (I've just entered my own postcode. While people can send me gifts, such as pot plants, there are no cut flower deliveries available here through Interflora).
Most other online services use local florists to make their deliveries, so you probably won't find much difference if you try other websites. eFlorist though is still offering to deliver flowers from Monday onwards:
https://www.eflorist.co.uk/