two SWT trains,
 

hi.

Dunno if anyone can help, on monday night, a SWT class 159 appeared to be towing a SWT class 158 or 159 from Bristol to Sailsbury.

Can anyone provide me with details to why there was two units instead of the usual one, also their numbers if possible. Did one fail in bristol and another was sent to collect it acting as a late running SWT service back to Sailsbury in the process?

Any help would be greatful in knowing what this observation was.