Well, considering semi-automatic rifles and handguns in the UK are banned, maybe legally they could have gotten their hands on like a hunting rifle and shotgun (maybe still double-barreled), not sure if the death toll would still be the same or heck, an even lower kill count (which for some reason would sound realistic for such an attack in 1999 England to me). Unless if in such an alternate universe/reality they still break into a van and steal shit and are prohibited, maybe they could just obtain guns illegally, but of course theres always the possibility of them failing and getting caught trying to buy guns off the black market.
_________________
"I'll never understand humans. The way they live their lives, their feelings, the things they want to do in life, probably has something to do with these
invisible gods they pray to. Meh" - Kimveer Gill
"Humanity is overrated, isn't it?" - Matti Saari
"Live in virtue, no desire
And in the grave an angel's choir
You look to heaven and wonder why
No one can see them in the sky
Just as the clouds have gone to sleep
Angels can be seen in heaven's keep
Alone in fear, they question why
Goddamn, not an angel when I die" - Engel, Rammstein (English version)