Hi, well I think I'd wait til you can plant them outdoors this spring (after the last frost has passed), and grow them in the ground where they'll do the most the fastest. You didn't say if you were e.g. in the Hebrides vs. Cornwall (where it's a lot warmer!). If you are in the south, maybe a grower there could tell you how hardy the plants are in your area, whether they can live outdoors all year or not, or how much protection they need over the winter - they're not really meant to grow indoors and they do get awfully large. Otherwise, it is best to grow them out individually for as long (couple of yrs?) as it takes for you to be happy with the trunk growth, etc.

Shame I have already begun the propagation process in a dark and warm place but we're close to spring anyway. I am currently living in the north (Newcastle Upon Tyne) but will be moving south after the summer (Kent) Placing them outside isn't an option at the moment. You said they aren't meant to be grown indoors but do you think they`ll cope?

Yes, now that they're started there, and it would be too cold outside. I'm not sure even that Kent would be a good idea year round (lucky you tho!). Be sure you have them in a gritty well drained mix and give them as much 'high' light as you can all day.