Nearly there. 11a Extreme leftists in campaigning have influence on some island (5) C - I - S
10a Second-floor room with cracking ceiling and draught (3, 4) T - O - A - R
I can only think of TWO PAIR, but I can't see why.
26a English blocks unlaid, originally from another source (7) A - I - - - -
Thanks for any help.