Hard to be prescriptive without knowing what plant they are - I guess just multi purpose compost. Again, without knowing what they are, hard to say whether you need to keep them indoors all the time or just through nine months of year other than summer, or whether they'll do okay outside.

Could you add a photo to your question - might give us a chance to i.d. then we can give you better answers.

Many thanks for your answers, I have stretched my computer skills to the limit and added a photo, hope this helps.
Also as it's probably a semi-tropical plant, how often would they need watering?
Thanks again.
John H.

Thanks for the photo Jonix, unfortunately it hasn't helped me to i.d. the shrub.

They look like Crassula's (Jade plants) to me,but can't see them as a hedge...are the leaves quite thick,and smooth to the touch ? Nothing else comes to mind,sorry....

I'd use standard potting compost but try it with only one plant first.

as the soil there is volcanic I'd be tepmted to use a gritty soil/compost to ensure free draining conditions.

Good point Seaburngirl

I remember seeing these bushes at the Lido de Jessolo near Venice, but didnt know what they were. Might be best in a hotel foyer where there is central heating on !

As they are succulents and happy in Lanzarote I don't think they'll be hardy in a British winter. Succulents generally are designed for warm dry conditions and some will lose their leaves altogether in a dry spell and grow them again when it rains. I would treat them like cacti and water no more than weekly in summer and monthly in winter. As you have three you could vary what you do as an experiment.