I recently contact the Lancer Museum requesting information on the various markings and they have kindly replied
"....... Thank you for your email. It seems to us that the '17' is a Regimental mark and would refer to the 17th Lancers. The small letters could be SQN and
refer to Squadron. '05' & '90' could be dates when repairs were undertaken.
'T.P.' could be TP for Troop and would be with a letter such as 'A' or 'B',
Link to 17th Lancers ....... http://en.wikipedia.org/wiki/17th_Lancers
It would seem that these Lances may have seen / been at several historical battles