I received some vouchers from LU recently after 2 tube delays. The reverse
of the vouchers state they can also be used at Natioanl Rail stations in the
south east where part of the journey includes the underground.

However, I went to a major London terminal earlier (Euston), and the booking
clerk refused to accept the vouchers despite my ticket including
cross-London transfer. He didn't accept the condition on the reverse as it
was a tube voucher!

Who was right?