Peonies in London: a flower England has grown since the mid-1700s
Paeonia lactiflora, the source of most cut peonies sold today, reached England in the middle of the eighteenth century, and peonies in London still follow roughly the calendar that history set. British fields cut their own stems only from late April to June, and about nine in ten of the cut flowers sold in Britain come from abroad, so what a florist has on the bench depends on the month you order in.
Delivery across London is covered zone by zone on its own page, and hotel deliveries, hospital wards, ordering from abroad, the order calendar and what central heating does to cut flowers all have their place on hotels, wards and London's flower calendar.
Late April to June: when Britain cuts its own peonies
A peony bush flowers for only seven to ten days a year, which is why the British season is so short and so sharply dated: late April to June, then nothing until the following spring. For the rest of the year, these are flowers that travelled. The Netherlands supplies most of the cut flowers imported into Britain, at times as much as three-quarters of what comes in, and it happens to be the world's largest grower of cut peonies besides. Its own stems are cut in the same late-April-to-June window and stretched into the following months by cold storage rather than a longer growing season. The result is a flower you can find for most of the year, though not for quite all of it.
Out of season, a florist builds each bouquet to order rather than keeping peonies on standby. If the particular variety or shade asked for isn't available that day, it's swapped for one close in colour and price. The swap is visible on the photograph taken before the courier leaves, so there's time to ask for a change before the bouquet is on its way.

English peony-shaped roses beside the real thing
A peony-shaped rose is usually an English variety, most often one of David Austin's, bred to open into the same full, many-petalled cup as a real peony. It shares a birthplace with the flower it resembles. Several bouquets set the two side by side rather than asking you to choose between them. Duo of Peony Roses and Peonies pairs a peony with a peony-shaped rose in the same hand-tied bunch. English roses and other peony-shaped varieties make up a section of their own for anyone who wants the rose on its own.
For a single-flower bouquet with nothing to compare it against, there's 11 White Peonies with Eucalyptus: eleven stems with eucalyptus worked through as filler rather than a second bloom fighting for attention.

Thirty-five stems, a basket or a box: sizing the gift
The quantity runs from a small hand-tied bunch up to Bunch of 35 Peonies, an armful rather than a bouquet in the ordinary sense. Counting stems carries less weight in Britain than it does elsewhere: a dozen is an entirely ordinary size to send here, not a number chosen to avoid.
A basket or a box carries its stems in soaked floral foam rather than a vase, which is what lets either stand on a table with nothing underneath. The foam wants a thin, even watering over its whole surface every day, not a single pour in one spot. A peony bought as a tight bud opens fully over a day or two somewhere warm and bright, and from there holds for five to seven days with that care; central heating works against it, as it does against most flowers kept indoors here.
Peony delivery in London costs nothing extra in the centre, and the time any particular bouquet takes is shown on its own page rather than promised in the text.
Start with bouquets with peonies for the pairing with a peony-shaped rose, or go straight to peonies by quantity once you know how many stems the gift needs. For a table rather than a hand, baskets with peonies and boxes with peonies stand on their own, foam and all, wherever they're set down.