Bell resumed on 95 not out and soon past the hundred mark and then the two hundred mark. He had reached 215 in only 288 and had hit 34 fours when he was caught by Banerjee off the bowling of Marshall.
Bell lost his wicket with Warwicks only two runs behind Gloucestershire's total of 336 and with Jon Trott going onto make his century, Warwicks at tea were 409-4 having lost Jim Troughton for twenty.
In the final session,Warwicks lost three quick wickets with Frost,Botha and Carter all going cheaply. Ian Salisbury, made 48 including two sixes whilst Trott at the other end, passed the 150 mark.
Warwicks were now knocking up their biggest score of the season and declared on 528-8 with Jon Trott not out on 164 from 247 balls and Chris Woakes 17 not out.
Gloucestershire, needing 192 to avoid an innings defeat, were given ten overs before the close. They managed to survive the attack of Martin, Woakes,Botha and Salisbury and closed on 36-0.
The final day is tomorrow and play is due to start at 11am. Commentary on the game can be heard via the BBC Coventry & Warwickshire website.
On Friday, Darren Maddy is expected to make his Warwickshire comeback in a second X1 game against Somerset. The game will take place at Coventry & Warwickshire's Binley Road ground.