I email'd BA to ask what happens to points on joing the ECCCA and this is what they had to say:-
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">May I advise that on transferring to your company's Corporate Agreement your Executive Club Points total will be reset to zero however, your membership tier status will remain the same. Also, your membership year and expiry date will be brought in to line with your company's Corporate Agreement.</font>
This kind of put paid to my plans of switching in the hope of extending my points gathering year! My tracking year ends in December while my company tracking year ends in August. I'll easily do my 500 points before December (I have 490 so far) and given that there is no reduction in the amount of points required for Gold I see little point in switching. Now if BA reduced the qualification level for Gold to 1200 it may be worthwhile!