The service fleet has been tracking on Bus Times since the start of the year and earlier this week, fleetnumbers have appeared on there:

Optare Solo
YDZ533 (MX07JOH) is listed as number 2
LJU914 (MX58ACO) is listed as number 6
YJ11OJK is listed as number 20
YJ12GZL is listed as number 22

E200
YX17NTT is listed as number 5
YX17NDY is listed as number 7
YX17NTO is listed as number 8
SN65OHE is listed as number 9
YY66PCZ is listed as number 12
SN59AXB is listed as number 16
KX58GUU is listed as number 21