Sandy's in Twickenham) sold their own, homemade version (along with a great selection of other sausages, including boerwoers, venison and cajun - great for barbecues!). I have also found merguez sausages at the Whole Food Market, Kensington, and in various Middle Eastern delis and supermarkets on Goldborne Road (good for Middle Eastern ingredients generally).
Chakchouka is a popular breakfast dish in north Africa, and there are several variants. For vegetarians, you can of course omit the sausages. I love the eggs which are cooked on top of the ragu of tomatoes and peppers, and I sometimes add slices of Halloumi, that squeaky Middle Eastern sheeps' milk cheese. I serve Chakchouka with fluffy couscous and no Middle Eastern supper would be complete in my house without the obligatory jar of Belazu Rose Harissa.
Chakchouka for 2
6 merguez sausages
1 large red or orange pepper, or 2 small ones
1 400g tin chopped tomatoes
A little Harissa paste or chilli
1 tsp ground cumin
Salt & pepper
Harissa and chopped fresh coriander to serve
Just before you are ready to eat, break the eggs over the top of the ragu and continue to cook until the eggs are set (I like mine just done). Serve with fluffy couscous, or flat breads, and lots of harissa and fresh coriander, if liked.