Paul Oter wrote
[...]
I explained the problem to my employer's accounts department and they
said that they were happy for me to claim without a receipt.

(To avoid this complication I asked Cambridge ticket office to sell
me
a through ticket from KX (LU) to my destination in Berkshire. However
I
was told that such a ticket doesn't exist, and that they could only
sell me a ticket starting at Waterloo)

My local SWT station out in Surrey beyond the Travelcard area was happy
to sell me a single to Waterloo plus Underground Z1 for today and
another single + Z1 dated 3 days later for my return trip. They said
they had had some reports of problems with the automatic barriers for
the future dated U1 tickets but in fact I had no problems to/from KX.

When I worked for BP (before 1999) the expenses rules said that no
receipt was expected for journeys of less than 50 miles by public
transport.

--
Mike D