BBC News Online investigates why the operator on some of the UK's worst performing rail franchises is receiving a sweetener rather than a rebuke.

Virgin Rail, billionaire Richard Branson's train firm, getting �100m compensation? That's a bit rich.

Well, for a start Virgin Rail does not just belong to Sir Richard. Stagecoach has a 49% stake.

And secondly, it is not compensation but an "interim agreement", according to the Strategic Rail Authority, which has brokered the deal.

But, yes, �100m is a huge sum, especially at a time when the UK's transport network is screaming for investment.

So why, pray, has the award been made?

Anyone who has been kept waiting for a UK train will be aware of the spat between the train operators and the separate firm - until recently Railtrack - which maintains the tracks and signals.

Operators would blame Railtrack engineering works/signal failures for delays.

Railtrack, meanwhile, would accuse operating companies of running dodgy rolling stock.

Whoever is to blame, just two thirds of trains on Virgin's London-Glasgow and Dundee-Penzance routes have been running on time.

But Virgin has sought - to government applause - to distance itself from the hoo ha through upgrading its fleet, in a �2bn investment programme.

Spearheading the project are 55 tilting, Pendolino units, capable of travelling at 140mph, and reducing the journey time from London to Liverpool to less than two hours.

But while the trains have begun to arrive - the first enters operation on Tuesday - track improvements allowing them to run faster than 110mph have not.

So what?

So Virgin will not be able to run the London-Glasgow service in under four hours, as it had planned.

Hence it will not win the improved passenger numbers it had hoped for, nor be able to increase train frequency.

What is more, Virgin services - and passengers - have yet to suffer the full effect of disruptions bound to be caused by engineering work.

But I though Britain's railways had been privatised. Why should taxpayers be forking out?

Virgin chiefs have, unsurprisingly, held Railtrack, a private firm, responsible for the track upgrade delays. And they have demanded compensation reported at more than �250m.

However, Railtrack was pushed into administration by the government last year.

And its successor, Network Rail, is state owned.

So the case could not only end up at the government's door, blight the early days of Network Rail and prove more expensive than the �100m.

It could also provide little reward for a firm which has kept its side of the new deal for UK railways.

The SRA claims it has also been able through the negotiations to wring assurances from Virgin regarding, for instance, service guarantees and access to projection figures.

It is as yet unclear whether these are anything but token compromises within the interim �100m agreement.

Interim agreement? Does that mean there is more cash to come?

A good question, and one the SRA declined to comment on to BBC News Online.

Monday's deal commits to providing Virgin Rail with "short term financial support".

In the rail world, where companies use 40-year-old rolling stock, where it can take a decade to open to a Channel Tunnel rail link, when "short term" could end is anyone's guess.

What it does allow is warmer relations between Virgin and SRA chiefs as they renegotiate the operator's two franchises in the light of the new West Coast main line reality.

"[Monday's deal] delivers stability while the SRA works with Virgin Rail Group to identify and secure the best future for passenger service and delivery," SRA chief operating officer, Nick Newton said.

Some reports say this will lead to the injection of a further �230-450m in Virgin.

The SRA has said that, ahead of any formal franchise agreements, such talk represents speculation.