A part suspension on the Piccadilly line is causing delays following a signal failure at Hyde Park Corner.
In addition, there are severe delays across the rest of the line.
Transport for London is warning tube users not to use the Piccadilly line as trains are likely to be very crowded.
Tickets are being accepted on local buses and the Great Northern service.
We will be bringing you all the very latest updates, pictures and video on this breaking news story as it develops.
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Hurrah! Good service
There is now good service on the whole of the Piccadilly Line.
Good and bad news to report
The delays are now only between Acton Town and Heathrow Terminals/Uxbridge
Elsewhere on the line
There are also severe delays on the London Overground, with TfL reporting:
Severe delays Liverpool Street to Chingford, Cheshunt and Enfield Town due to an earlier track fault at Liverpool Street. London Underground accepting valid London Overground tickets via any reasonable route. GOOD SERVICE all other routes
The latest on the Piccadilly line:
Severe delays Acton Town to Heathrow all terminals and Uxbridge due to an earlier signal failure at Hyde Park Corner. MINOR DELAYS on the rest of the line. Tickets are being accepted on local buses and Great Northern
There is also minor delays on the Waterloo and City line due to an earlier faulty train
It's still not perfect...
As we head towards the evening rush hour...
There’s this from TfL. It’s doesn’t make the best reading for commuters
All destinations on the Piccadilly Line are affected
Commuters warned to re-plan journey
The Piccadilly Line status is still reporting ‘severe delays’ after the earlier fault.
TfL are still reporting severe delays on the Piccadilly line.
'Hell on earth'
Seen it all before...
Rayners Lane update
The signal failure problem on the Metropolitan Line has been resolved and services are back to normal.
However, the Piccadilly line is still experiencing severe delays.
Rayners Lane signal failure
A second signal failure on the tubes is causing further delays for west Londoners.
While severe delays continue on the Piccadilly line, there are now minor delays on the Metropolitan Line between Harrow on the Hill and Uxbridge due to a signal failure at Rayners Lane.
Piccadilly line update
Severe delays continue throughout the Piccadilly line following an earlier signal failure at Hyde Park Corner station.
Stations beyond Rayners Lane
People travelling to Uxbridge are advised to take the first train that arrives on the platform to Rayners Lane and change at this station for services onwards to Ickenham, Hillingdon and Uxbridge.
Severe delays continue
Piccadilly line services are up and running but with severe delays across the entire line following an earlier signal failure at Hyde Park Corner station.
Use alternative transport
People are urged to continue to use alternative modes of transport including local buses and the Great Northern railway service where tickets are still being accepted.
While Hyde Park Corner stations has re-opened to the public TfL has advised tube users to continue to avoid the Piccadilly line due to overcrowding and longer journey times.
Eastbound services - part resume
Part of the Eastbound service has resumed.
However there continues to be no service between Finsbury Park and Cockfosters - eastbound only.
Severe delays remain on the rest of the line.
Hyde Park Corner station has been re-opened following an earlier signal failure which continues to cause chaos on the London Underground.
Avoid Piccadilly line
TfL continues to advise people NOT to use the line if possible due to overcrowding at stations and longer journey times.
No Eastbound service
There is still no service Hammersmith to King’s Cross eastbound on the Piccadilly line.
Severe delays continue on the rest of the line.
Westbound services resume
Services on the Piccadilly line between King’s Cross station and Hammersmith station have resumed - westbound only.
The Eastbound service remains suspended.
Hyde Park Corner station remains closed.
Re-plan your journey
Remember you can use the TfL Journey Planner tool to re-plan your route as chaos continues on the Piccadilly line.
Track work finished
Engineers working on the Piccadilly line issues this morning have completed the track work and testing is expected to begin soon.
It is not clear how long this will take to resolve.
Meanwhile the line remains suspended between Hammersmith and King’s Cross stations with severe delays continuing on the rest of the line.
Engineers on site
Engineers are on site at Hyde Park Corner station to resolve the signal failure problem which continues to cause travel misery for people on the Piccadilly line.
'Stuck for almost an hour'
Reports have been emerging on Twitter from people stuck on the Piccadilly line for almost an hour, while Acton Town station is in ‘carnage’
Travelling to Heathrow
If you’re travelling to Heathrow Airport then the advice is to avoid the Piccadilly line and use local buses or the Great Western Railway services from Paddington Station.
The Piccadilly line remains closed between Hammersmith and King’s Cross station with severe delays across the rest of the line.
Piccadilly line woes
Commuters have taken to Twitter to air their woes as the Piccadilly line is down this morning.
Avoid Piccadilly line
Tube users are urged not to use the Piccadilly line this morning following an earlier signal failure.