Why???

This year I have grown several different varieties of tomato and they are all doing well. The problem is only with Marmand they are all producing a mega flower at the growing point. Anyone know why this should happen and what should I do about it?
Thanks

I think they are called megablooms...other than that I can't help

AFAIK megablooms are most common on beefsteak type tomatoes. Two or more flowers will fuse together, each is pollinated separately but the tomatoes join together to make those big ugly fruits that win competitions for the heaviest tom!!
You can either nip the flowers off or leave them to grow a prizewinner. 
I remove them.