Actually there is a way to see the opposite Banks who trades with you at IB.View-Audit-expanded.
As far as i understand you will see every trade ticket twice, first every ticket with Barclay as executing Bank and then second the actual bank ,which means that they are using Barclay's always as their back door.
IB is a very solid and reputable broker the only downside ,their platform is for quick execution not suitable.
I recommend to use Currenex, as mentioned allready above, LCG is good downside atm no seggregated acc available .
BFL good excecution,(connected with New EDGE), but high commission.
Integral atm not connected with all liquidity providers .
Fixi is with UBS and also no seggregated accounts available.
so i would say you must decide between the best liquidity(Fixi/UBS,LCG/JP)and account security(BFL/New EDGE)