Many, many fine test trains!
New Measurement Train (NMT)
Stucture Gauging Train ( The death star!)
Track Recording Unit (TRU - the Class 950)
Mentor (OHLE Insecpction)
Track Inspection Coach (TIC)
I am sure an expert will be along soon to give you more information
Plus Track Recording Coach (TRC, formerly known as HSTRC in Research/Serco days), Ultrasonic Test Units 2, 3 and 4 (soon to be joined by 1), MPV, Radio Survey 1 and 3 (GSMR test vehicles). Loads of them. NMT is a mere trifle compared to some of the work the others do.