Sprouts are smaller than peas but plants are 3’ and full of green bushy leaves.
This article explains how to trim brussels sprouts for bigger and more sprouts:
https://www.gardeningknowhow.com/edible/vegetables/brussels-sprouts/pruning-brussels-sprouts.htm
In the south east of the UK
These articles should help:
https://www.gardeningknowhow.com/edible/vegetables/brussels-sprouts/how-to-grow-brussel-sprouts.htm
https://www.gardeningknowhow.com/edible/vegetables/brussels-sprouts
2 years in a row, I've had beautiful Brussel sprout plants , but have gotten 0 Brussel sprouts. Never have had an issue before this.
Unfortunately, there are quite a few reasons for this. Being in zone 6, you will need to be sure to plant these early enough to reach the 80 to 100 day maturity without exceeding temps between 70 and 80 degrees. High temps are a very common cause.
Next comes fertilization. They need fertile soils, especially nitrogen, in order to produce properly. An all purpose does fine.
Insect problems can lead to lack of sprouts, since it requires quite a bit of the plant's energy to fight.
This is true of infection as well.
https://www.gardeningknowhow.com/edible/vegetables/brussels-sprouts/no-brussels-sprout-heads.htm