Tax efficient business structure?

Hi

I am a sole practitioner, acting for the usual run of the mill small businesses and tradesmen. A relative has asked for advice in setting up a new business venture. 

There will be three equal participants in the new business, two UK residents and one French resident. The new business will potentially generate a high income and the participants are keen to minimise their tax liabilities, if possible making use of an offshore structure. I have little experience of this area of tax planning and would not normally take on such work. However, the family connection means that even if I do not act, I would like to point my relative in the right direction. Does anyone have any tax planning suggestions or can you recommend a specialist firm to contact who will not charge the earth for advice?

Many thanks.