At present, patrons are requested to stand on the right and overtake
on the left.  In 1927, it was also the case as shown on
http://www.suite101.com/article.cfm/london_underground/80615

I have colleagues that are certain that it has changed over the years,
as when they were in England from 1980-95 it was a "stand on the left
and overtake on the right" policy.

Can you please look into this, and tell me:
a) did they change
b) why did they change
c) if you can provide some evidence that they did or didn't change,
that would be great.

I'm afraid your colleagues have mis-remembered.  There has been no
change in policy, at least during the time I've been working in London
(between the early 1980's and now).

Michael2

Interestingly, this 1924 London Transport poster by Horace Taylor
seems to show an entirely different system - one escalator for walking
down, one for standing:

London Transport Museum
http://www.ltmuseum.co.uk/cgi-bin/shop.cgi?cmd=product&product_id=218&page=1&customer_ID=w1xDQwAA251263110972

Having travelled in London throughout the seventies and eighties, I
always remember the 'keep right' rule. LT have done some silly things
in their time, but arbitraily changing a rule like that just wouldn't
be cricket.

I commuted by tube into London between 1978 and 2001. I can assure you
there was never any change in the policy of stand on the right, walk
on the left. The word 'chaos' springs into mind.
answerfinder-ga

Having said that, there is a 'keep left' rule in many of the
passageways on the tube - perhaps your colleagues are remembering
that?

Dear GJLipman,

I've been travelling the London Underground since 1965 and can confirm
what others have said: that the rule has always been "Please stand on
the right".  (I assume that the reason for this is that more people
prefer to hold on using their right hand than their left.)  The
attachments bearing the signs on most escalators have the shape of a
triangular prism; they are known in the trade as "Toblerone signs",
after the chocolate bars.

My favourite advertisement of this rule was on a poster which I
suspect from its style was from the splendid 1930s period of
Underground posters, but I cannot trace it at present to confirm this.
 A rear view of a busy up escalator showed every step occupied by a
courteous traveller obeying the rule and standing carefully to the
right.  On the left was a solitary gentleman ignoring the rule: he was
wearing a large learner-driver's L-plate on the back of his jacket.

Carnegie