Removing self tapping masonry bolt trouble..

[Coaster]

I have a bit of a problem trying to remove 3 very large self tapping masonry bolts/screws which were fixed in to the middle of each brick. the bricks are on the corner of the wall. I'm not sure how long they are, but the heads are hex. about 15mm head, and protrude about 10cm
I have tried a spanner, but the force is twisting the shaft.

Could I just cut them off flush to the brick, or should I try to remove them totally? not sure if they would expand with rust and cause problems.

 

[Static]

Are they stainless steel? Also why do you need to remove them?

 

[Deluks]

Fence or gate post? Could grind or hacksaw them flush, but I can't see why they should be so hard to get out. Ring spanner would be better than open end.

 

[Coaster]

got them out this morning!
after reading your posts I had another go with a ring spanner as suggested, but used a LOT more force. I thought if the shafts shear, i'd just cut them flush to the brick. I can get the batten on for the gates now!
thanks for the help lads