OK, I'll do the best I can:
TW 98 is the part number used for the Grenade, Hand, Anti-Riot L1 series (L1A1 through L1A3).
DMB is Davies Metal Box who made the cans (in 1972).
GRENADE, PRACTICE, A/RIOT, S1A1 was believed to have been made by Schermully as a non-irritant practice version of the L1 Anti-Riot but was not adopted for British Service and I can't say that it was even trialled. It could have been a commercial contract for South Africa or the 'S' in 'S1A1' could have just been something to indicate Schermully.
The underlined 1 is the Lot number and 3/75 is the date of filling.
Unusual not to have Schermully, or PWS marking as the fillers.