National Rail Live Departures - Met line stations

I remember reading somewhere that NR includes all LU stations on it's database, each of them starting with Z. In about 1 minute of trying various combinations I only found one other, ZBK = Barking.

There has definitely been a thread on this forum (I can't remember where though, it was quite a while back) about interesting (ahem) routings across London from NR.

Why is it so hard to buy a ticket for Amersham at non-Chiltern/LUL stations, given that it has a code, one which isn't a 'Z' code, then?

@chris: the cross-London Maltese Cross marker on a National Rail ticket is very flexible. You can use pretty much any pair of Underground stations appropriate to the route between the National Rail stations. As I understand it, an example of Surbiton to Chingford could be valid by using Underground services between:
Waterloo and Liverpool Street (the obvious Zone 1 terminal-to-terminal route)
Vauxhall and Walthamstow Central (probably the quickest)
Wimbledon and Walthamstow Central (if you like tube trains)
Blackhorse Road and Walthamstow Central (if you prefer the NLL and the Goblin)
Kensington Olympia and Liverpool Street (if you're picking up friends from the Great British Beer Festival)
or pretty much any combination of connections. I'm not sure how long this has been the case, rather than simple London Terminal to London Terminal connections - and note that some National Rail tickets disallow a useful Underground connection (e.g. Chingford to Stansted Airport is annoyingly not valid on the Underground between Walthamstow Central and Tottenham Hale, being 'Route Clapton' and missing the cross-London marker).

There is a full list - each Underground station is known both by a CRS three-letter code, and a four-number NLC code which I think matches the Underground's own numbering system used on UTS tickets.

@amershamsi: it certainly should be possible to but tickets from *some* National Rail stations to Amersham, which has a NLC of 0506 on the ticketing system. Not all stations have a fare available however, roughly speaking only those within around 30-40 miles of London - e.g. Winchester no, Basingstoke yes. Let me know if you're looking for prices for anything specific and I'll check.

@upfast: shhhhh!

I tried Euston (NR ticket office), wanting to make advantage of my YPTC not all that long ago. The guy was very sympathetic (lateish on a Sunday, no queue) but informed me I had to go downstairs and get a ticket there, as he was unable to sell me any ticket to Amersham (including a travelcard, at that point to 'D').

The guy that I asked at Southampton Central completely failed to understand. After that, I realised that a ticket from Southampton to Great Missenden was 50p cheaper than a Southampton to Waterloo ticket, and then PAYG to Amersham (now YPRC is usable on Oyster, the disparity would be gone).

It's absurd that I can buy, at Southampton Central, a ticket between Dovey Junction and Wick - two fairly lightly used stations many miles away from Southampton, yet can't get a ticket all the way home, due to home being a 'no mans land' of an LU station (served by NR trains) outside of zone 6. Fantastic integrated ticketing that I have to change tickets at Waterloo!

It doesn't matter that much, as unless I want to break my journey in London, I go to Slough and get a lift from there, as it's quicker and cheaper.

Edit: As for why Croxley might be on there - perhaps it's planning for when the Croxley link is on there (and the station may be served by Chiltern trains), or because of the closure of Croxley Green.

Please do tell more! I know there were some tickets available after closure for travel to/from Mill Hill The Hale via MHE and a local bus, perhaps limited to existing season ticket holders?

Quite - that's why I quoted an example ticket that does have a Permitted Route via the NLL and Goblin (Surbiton to Chingford) rather than a ticket that doesn't!

I wouldn't suggest trying to travel (for example) Surbiton to Croydon via the NLL to Highbury then going back south on the Victoria line, because the Permitted Route couldn't take you north of Olympia. One thing I've noticed however is that there are three routings for Surbiton to Croydon Stations tickets: "NOT LONDON" "+LONDON NOT UND" and "+ANY PERMITTED".

Given that the + (Maltese Cross) is a specific indicator to show validity on Underground services to cross London, what does the second route actually mean? I always change at Clapham Junction anyway (it's the cheapest, Not London route), so have never needed either of the other two.

Sorry for going off topic!

Wiki has a lot of the NR station codes for LT stations on their respective pages.