All of them actually, it was the entire new build fleet of RJ100s that had been operated from Gatwick. So aircraft, callsign and livery, and surely some crew as well?
There were 2 RJ85s, not from Cityflyer Express, but on checking they turned up the following year. Livery is a very tenuous point, it's the BA livery. Definitely not crew. Cityflyer Express crew became part of the LGW mainline operation in 2001. The RJ100s when they moved to MAN/BHX were flown by the previous MAN/BHX mainline pilots who had previously flown the 737/A319s respectively.
In the intervening years between 2001 and 2007, operation of the RJ100s became part of the BA CitiExpress/BA Connect fleets, and crewed by their pilots.
6 years later when BA Cityflyer was formed out of the former BA Connect, that's how the RJ100s were able to retain the 110 seat configuration; they had previously been a mainline aircraft. The new E190 fleet was restricted to 99 seats by scope.
Regards