Was the OP originally booked on EU airlines (or airlines of nonEU countries that follow the EC261 regulations)?
OS is an EU airline.
but since GB doesn't have airside transit in T2 the passport validity became an issue.
T2 offers airside transit. You can even transit airside between T5/T4/T3 to T2 or the other way around, without having to go through passport control. You just need to clear security at the respective flight connection center in T2.
My nine years old son passport was three months before expire and we couldn't go to London they denied is the boarding for London .
I am also not quite sure about the passport expiry requirements for airside transit passengers in the UK. However, it is worth investigating, whether the LH gate agent in MUC handled the situation correctly. If the son met the transit requirement in theory, then the OP could claim EC261/2004 compensation also from Lufthansa for denied boarding.
I am checking TIMATIC.
National Albania (AL) /Embarkation Albania (AL)
Transit United Kingdom (GB) /Destination USA (US)
ALSO CHECK DESTINATION INFORMATION BELOW
United Kingdom (GB)
TWOV (Transit Without Visa):
Visa required, except for Passengers holding confirmed onward
tickets making an airside transit at London Gatwick (LGW),
London Heathrow (LHR) or Manchester (MAN) on the same calendar
day to a third country (excluding Ireland (Rep.)).The
following conditions must be complied with:
- passenger must arrive and depart by air; and
- passenger only intends to transit through the United
Kingdom; and
- passenger must hold all documents required for the next
destination; and
- passenger must not leave the transit area; and
- passenger travels with a document listed in the following
warning(s):
- ***Warning*** Passengers may make an airside transit if
holding a valid entry visa issued by Australia, Canada, New
Zealand or USA. (SEE NOTE 57398)
NOTE 57398: E-visas or e-residence permits are only
accepted for airside transit when the airline is able to
verify it with the issuing country.
- ***Warning*** Passengers may make a airside transit if
holding a valid "D" visa issued by an EEA Member State
For details, click here or Switzerland. (SEE NOTE 57398)
NOTE 57398: E-visas or e-residence permits are only
accepted for airside transit when the airline is able to
verify it with the issuing country.
- ***Warning*** Passengers may make an airside transit if
holding a valid biometric visa issued by Ireland (Rep.)
endorsed "BC" or "BC BIVS" in order to transit to a
destination other than Ireland (Rep.). (SEE NOTE 57398)
NOTE 57398: E-visas or e-residence permits are only
accepted for airside transit when the airline is able to
verify it with the issuing country.