Ian Tomlinson v Alex Thomson - narrative
This is an attempt to compile a comprehensive narrative about the situation around Royal Exchange when Ian Tomlinson was assaulted, and subsequent events, referenced to photos, videos and eyewitness accounts. It is still very much a work in progress, and will be updated frequently as additional material is located.

In the early evening of April 1st, on Lombard Street, where Ross Hardy and another unnamed photographer took pictures of Ian Tomlinson outside Gym Box, cops are clearing the street, and based on later videos some of those present end up on Cornhill. (cf. 1, V2-dhighbury)

Nearby on Cornhill a group of British Transport Police (BTP) and Met Level 2s split the crowd arbitrarily into 'protesters' and 'onlookers'. Present at this point are City of London Police Chief Superintendent Alex Robertson (CSAR - bronze commander for Operation Glencoe), a Chief Inspector from Sussex Police (KBCI - apparently CI Mills of EDO infamy), and several FIT officers of interest (F1 - EK127 PC Alan Palfrey, F3, & F4). (cf. 1, 2 - 7:11pm, 3 - 7:12, 4 - 7:12, 5, 6 - 7:15, 7 - 7:15, 8 - 7:15, 9 - 7:15, 10, 11)

Minutes later some of the FIT have moved from Cornhill to Threadneedle Street. Present are police dogs, Officer A, F3, F4, and a City midranking officer carrying a blue folder (CPblue). Two men are bitten by the dogs, one of them is arrested, and the FIT push photographers Eastwards, away from that branch of RBS, a line of Level 2s from Hackney (GD) arrives and runs towards Royal Exchange Avenue, while other officers move towards Royal Exchange Buildings. (cf. 1, 2, 3, 4, 5, 6)

Some of those officers emerge from the crowd on Cornhill, after what looks like a snatch arrest. Officer A and C1 appear to be involved. (cf. 1)

They retreat onto Royal Exchange Buildings where several people are struck with batons, and one person is thrown to the ground. (cf. 1, 2, 3, 4) A Met Level 2 Inspector is seen at the South end of Royal Exchange Buildings (cf. 1 - 7:18)

Officer A assaults Ian Tomlinson at the South end of Royal Exchange Buildings. He is helped up by demonstrators while F1, F2, F3, F4, C1, the dog handlers and some Level 2s look on, as he walks away the CPblue is seen coming to Cornhill from Threadneedle Street. (cf. 1 - 7:19, 2, 3, 4, 5)
On Cornhill some of the 'onlookers' sit down in front of a police line which includes BTP and Level 2s from Hammersmith (FH). CSAR deals with them personally, while CPblue is behind the police line. (cf. 1 - 7:17, 2 - 7:18, 3 - 7:23, 4 - 7:24)
The BTP on Cornhill begin to push the 'onlookers' Eastwards, towards Bishopsgate/Gracechurch Street. (cf. 1, 2, 3)
Ian Tomlinson collapses outside 77 Cornhill, some of the onlookers given him first aid before the police push them away. (cf. 1, 2)
The BTP are joined by the same City Police dog handlers seen on Threadneedle Street and Royal Exchange Buildings. The dogs are used to drive people Eastwards (cf. 1, 2 - 7:30, 3)
The dogs are moved behind the line of BTP, where there are also a group of FIT. (cf. 1 - 7:32, 2, 3 - 7:34)
When they reach the junction of Cornhill and Gracechurch Street the BTP stop in a solid line at the East end of Cornhill, and when two ambulances arrive the police remain across the road at first, one officer waves them towards Threadneedle Street, while people shout at the police to move. CSAR is seen personally directing the ambulances down Cornhill. (cf. 1, 2, 3, 4, 5)
Three Met vans drive up Gracechurch Street from the direction of London Bridge. Flour is thrown at them and they turn back. (cf. 1)
The police continue to herd the group which began at the Royal Exchange, now down Gracechurch Street, at Leadenhall Market there is an exchange of words between drinkers outside a pub, and the crowd, the FIT - with F1 among them - step in to keep the two groups apart, until a group of Level 2s take over. (cf. 1 - 7:46)
A serial of TSG join the BTP and the crowd is gradually moved all the way down Gracechurch Street, and then across London Bridge. F1 is seen with Steve Discombe on the bridge. (cf. 1 - 8:08, 2, 3, 4)

Key people seen elsewhere:

CSAR was seen directing the cordons around RBS (1, 2)

He was also in charge at the April 2nd memorial demonstration, and again on the April 11th justice march. (links?)

KBCI was also involved around RBS (1, 2, 3)

F1-4

Bartholomew Lane F1 – Alan Palfrey 
Bartholomew Lane - F1 - Steve Discombe - g20 protests 
Queen Victoria Street - Steve Discombe - F1 - Police Line 
Queen Victoria Street - F1 – 01042009602 
Queen Victoria Street - F1 - Getty Images - Mass Protests Are Held During The G20 World Leaders Summit 
Bishopsgate - F4 - pesky porkers 

F3
 
F1 Palfrey on April 2nd (1, 2)

C1

C1 - Bartholomew Lane

Notes:
All times quoted are either taken or calculated from photographs showing the East-facing clock on the Cornhill side of the Royal Exchange, which was checked as within 30 seconds of UTC on April 3rd, 2009.
Most of the identifiers (F1,F2,etc.) used were taken from Bristle's blog http://tr.im/iWQd.
To be incorporated:
http://www.youtube.com/profile?user=davehighbury&view=videos