Mike Ashworth is potty about the Tube. As London Transport Museum curator for over 15 years and London Underground Public Private Partnership (PPP) infrastructure curator since 2003, he is a man who knows his Charles Holden stations, Stabler tiles and Johnston roundels.
The best thing about the Tube's heritage, he says, is that Londoners do not have to visit the museum to appreciate it.
'You just have to glance up when you're standing at a station.' Growing up in Lancashire, Ashworth has a love of industry and engineering - 'I was a keen bus preserver' - and working in a 'contemporary' museum is his dream job. His role at London Underground involves more than just preserving the Tube's architectural heritage.
He is equally passionate about protecting its structure, especially where construction techniques were employed for the first time.
The London Underground is the world's oldest mass transit railway, dating back to 1863, and uses some of the earliest modern concrete, tunnelling and underpinning techniques.
When London Underground handed over maintenance and upgrade of the network to the PPP infrastructure contractors (infracos) the Transport Museum worried that it could lose some of its influence over the railway.
So Ashworth's first job was to produce a 'railway heritage features register'.
This is an aide memoire for the infracos during the early stages of planning station upgrades. All plans include a heritage strategy to protect features such as ceramic wall tiles and signage, Ashworth explains.
'Over 50 of the 275 stations are listed buildings.' He describes Sudbury Town station, designed by Charles Holden, as a structure which redefined the London streetscape, so any changes to its layout would be examined very closely.
Ashworth now gets stuck into station modernisations very early on to ensure the infracos know the relative importance of historical features.
'But we do realise we have to balance the needs of preservation and a 21st century railway, ' he says. The Disability Discrimination Act requirement for step-free access will be the main reason for modifications to all stations.
Ashworth is also keen to preserve one of the world's first Greathead shields - predecessor to the tunnel boring machine - which is lodged into the tunnel wall of what now forms part of the Northern Line (see photograph). The shield was designed by James Henry Greathead.
'What fascinates me is that so much of the history is in use and, if it's environmentally secure and doesn't conflict with modern operations, it'll stay where it is.'