On the right is a Matilda I. This was a two-man 'light' tank with thick armour. The whole light tank concept was discredited in the Spanish Civil War but the BEF was still stuck with some. It was armed with a Vickers MMG. Some were upgraded with Heavy MGs to give them some small armour piercing capability against other light tanks. It was painfully underpowered and slow.
On the left is a real tank, the Matilda II, Queen of the 1940 battlefield. It's pluses included a three man turret, heavy armour and a decent gun, the QF 2 pdr, that could defeat any German armour. On the minus side it was a bit slow - not really a problem in itself.
Its major drawback was that they were not issued with HE shells so were helpless against AT guns. This was not a problem given its thick armour until the Germans started using '88mm Flak cannons. An HE shell existed for the 40mm 2pdr but was never issued, apparently on religious grounds since everybody else issued HE shells for tanks with this calibre gun.
Of course, the T34 was going into production in Russia, sloped armour, 76mm dual purpose gun, wide tracks, high mobility, etc etc, but Russia was just plain ahead of everybody else.
