I just discovered this thread - great subject matter!
A few things from my perspective...
1. Like many countries, Britain had the wrong armour doctrine, dividing tanks between 'cruiser' ('cavalry' in other countries) and 'infantry'. It is unlikely Britain changes such doctrine before WW2.
2. The 2 Pounder was an excellent gun "in its day". Unfortunately, the emergency after the Dunkirk evacuation compromised the switch to the 2 Pounder's successor - the 6 Pounder. From mid-1940, for almost a year, Britain focused on producing "existing types", largely to the exclusion of new developments. The 6 Pounder was frozen and arrived several months too late. It is a tragic irony that there was a modern naval 6 Pounder available slightly BEFORE 2 Pounder was developed. the "6 Pounder 10cwt" was a twin, semi-automatic weapon designed for gun boats or coastal defence. It's official muzzle velocity is low - about 720m/s, but that might be due to requiring flashless propellant (the Navy used adapted 6 Pounder anti-tank guns with muzzle velocity reduced to 655m/s!) The 6 Pounder 10cwt has a propellant cartridge 464mm long and 79mm in diameter - compared to the Army 6 Pounder's 441mm by 90mm. This dimensions suggest a 6 Pounder 10cwt cartridge has propellant volume up to 20% less than the Army 6 Pounder, meaning a muzzle velocity about 10% less. The early Army 6 Pounder fired 6.3 pound AP shot at 2700f.p.s. through a 43 calibre barrel, pentrating 62mm of 30 degree armour at 1000 yards. 6 Pounder 10cwt should deliver 2430f.p.s. through the same barrel, penetrating 50mm; but 6 Pounder 10cwt used a 47 calibre barrel, probably increasing velocity to almost 2500f.p.s. and penetration to 53mm. Such a 6 Pounder would be devestating prior to 1941 and remain competitive until late 1942. How about adapting the Navy 6 Pounder in the same timeframe as developing the 2 Pounder from scratch? A better gun for less money - and British-developed!
3. Sometimes, possibly due to the lack of a Tank Board, the Brits were just plain incompetent. There are many examples (sticking radiators on the front deck of Covenanter!) but one that sticks in my craw is the blithe assumption that Cromwell, with its tiny 57.2 inch turret ring, would be able to accommodate the "75mm High Velocity" gun being developed by Vickers. Just to be clear: the Vickers HV (which would eventually emerge as the "77mm" firing 17 Pounder ammunition at lower, but still impressive, velocity was clearly going to be a powerful gun: muzzle energy would turn out to be close to 2400mj, almost twice the US M3 75's 1300 and more than twice that of the 6 Pounder. Cromwell prototypes arrived from early 1942 - and nobody (it seems) wondered whether a 57.2 inch turret ring, only slightly bigger than the 54 inch early-war British standard (which could accommodate 2 Pounder plus 3 men) could REALLY accept a gun almost four times as powerful as 2 Pounder and more than twice as powerful as 6 Pounder??!! It was not until mid-1943 that the mistake was realised and Comet hurriedly developed - just in time to be too late to make much contribution on the battlefield!
4. British engines. Grrr...At least their small diesel engines were reliable! Lord Nuffield should've been told to take his Liberty production licence and run away! Small diesels were available in a variety of power sizes in the late 1930s...examples included the 86hp 4 cylinder Perkins, AEC engines of 87, 105, 131 and 158hp and Leyland's 95hp. Matilda II was powered by a pair of 87hp AEC's, for example. Cruiser tanks should've shunned the Liberty and gone for a pair of diesels - for example, give an A13 two 105hp AEC's and it will deliver a top speed of more than 30m.p.h.
5. British suspensions - Christie too complex, almost everything else was poor off-road (and not very good on-road!) Then Centurion appears, with (British!) Horstmann bogies. When the Israelis ultimately give Centurion the right engine (750hp diesel in a 54ton tank - 13.9hp/ton) they get 28m.p.h out of fairly simple British suspension! Early Cruiser tanks really needed torsion bars (which existed but were hardly ever used by the Brits) and Infantry tanks needed Horstmann bogies (raising top speeds to 20+m.p.h.)
6. The A13 II through Crusader turret shapes! Those shot-traps under the inwards-sloping armour sections! Give all early British tanks the Valentine turret: too small, only fit for 2 men but cheap, simple to make and vertical sides! Cruiser tanks get the same turret with reduced armour.
So, early war tanks have "6 Pounder 5.5cwt" guns: AEC or Leyland diesels (singles in Infantry tanks; pairs of slightly smaller engines in Cruisers); sensible engine ventilation; Valentine turrets (57.5 inch ring diameter, able to accept US 75mm mid-war) with varying amounts of armour and either torsion bar or Horstmann (2-wheel bogies!); torsion bar (Cruiser) or Horstmann 2 wheel bogie (Infantry) suspension. When the "2nd generation" tanks (Cromwell and Churchill - Churchill isn't "ordered off the drawing board" post-Dunkirk, production of existing designs is prioritised) appear, some engineer produces a slide rule and determines they must have 64 inch turret ring diameter from the start!
By the way, read "Death by Design" by Peter Beale. He's far less sympathetic to the British tank industry than David Fletcher.
