With a bit of time on my hands today, I've done a bit of research...
I am going to try and list the locomotive types in use on the present day railway, although some of the photos may be of preserved locos for illustration. Also, don't pay too much attention to the liveries, as some of these are not currently used and the photos don't show every different livery.
There are two main types of locomotives in use on Britain's railway network - diesel shunters and main line diesel & electric locomotives. In the past, every major station would have had one or more shunter on station pilot duties, but these days they are confined to marshalling yards and depots and are much reduced in number.
The BR class 08 diesel shunter was introduced in 1952 as a development of the LMS design (BR class 11). The class 08, 09 & 10 were outwardly similar in appearance, but the 08 was the most numerous totalling 996 locomotives.
https://en.wikipedia.org/wiki/British_Rail_Class_08
Current operators on the national network include:
Network Rail (NR), Great Western Railway (GWR), Scotrail (ScR), Wabtec, East Midlands Railway (EMR), Freightliner, Eurostar, West Midlands Trains (WMT) & Derby Works. Others are owned by leasing companies including Harry Needle Railroad Company (HNRC), Rail Support Services (RSS) & Railway Management Services (RMS) - these can be found on hire to mainline railway companies, industrial users or preserved railways.
A large number have also been preserved.
Tony