Modern Railways a while back carried a photograph of this set at Topsham with a device attached to the front. In the Avocet Line Rail User Groups Spring 2019 Issue No 43 the relevant page from Modern Railways was reproduced.
It is in fact Fulgro's Rail Infrastructure Alignment Acquisition Platform. The device is fitted to service trains to measure track alignment with lasers. This reduces the workload on Network Rail's other test trains such as the NMT HST. I did not copy the article as it may infringe copyright.
Colas Rail Class 66 66848 was fitted with some similar gear when it visited Exeter (Central) in 2016 - photographs attached.