I have no doubt a clean (ie. no stores) Jag would make M1.0 at low level, but you would need a good run at it and as soon as you turn you’ll be quickly down to 400kts. The aircraft had pretty poor levels of specific excess power (SEP) as it was designed to be a trainer, but the Hawk took that role. Oddly enough I’ve been supersonic in a Hawk T1 as well, but looking at the slip ball we were going a bit sideways!
Anyway, if you want to go quick at low level, with live weapons then look no further than the F3 - just over 850KIAS at 250ft was the fasted I ever saw with a 2x2 weapons fit and she would have gone way faster if it hadn’t reached the edge of the operational clearance. She was still accelerating as she was throttled back at 850 and got towards 870 for a wee while as the engines spooled down.