Not many trees will appreciate being confined to a pot. I've dedicated trees in new woodland and in a green cemetery where I can always go and visit, you could consider something like that.

Thank you. I agree and we have an arboretum close by in a perfect location next to a river where we used to walk as children but they have stopped dedicating trees due to council cuts. :(

A laburnum will be relatively happy in a container - you just need to get the pot size right, potting on every couple of years until you get to the biggest container you have space for. Aim for a half barrel at least - an old dolly tub is ideal if you can get one or, if you are close to a brewery a large beer keg (preferably empty, haul it round to a friendly car repair shop - or anyone else with an acetylene torch - and ask them to cut off one end and cut some drainage holes into the other end). You should be looking at a container at least 2ft in diameter and about 3ft in height - you can allow the laburnum to spill over the sides.

There is a dwarf lilac that only grows to five feet - I think its called Pixie. You can also get small standards. have a lok on google for Dwarf Lilacs - here's one to start you off;
Vhttp://www.gardeningknowhow.com/ornamental/shrubs/lilac/dwarf-lilac-varieties.htm

Dwarf European Fan Palm, Chamaerops humilis

Thank you everyone for your help, it's very much appreciated and I love all your suggestions!