It seems like great news for anyone wanting to get around Britain more swiftly: Network Rail has outlined its plans for a high-speed rail link from London to Scotland. The case for such a scheme is powerful; rail capacity is close to bursting and Britain has been left trailing by other countries such as France and China. Here is the news story on the BBC.

Before you get too excited, however, here are a few reasons why the announcement is not quite what it seems.

1] Network Rail’s report is separate from – and could be irrelevant to – the feasibility study on high-speed rail being carried out by High Speed 2, a company set up by the government earlier this year. HS2 has cautiously described the publication as nothing more than a “useful contribution“.

2] HS2 is primarily focussed on a high-speed route from London to the West Midlands: a longer route up to Scotland is only its secondary consideration.

3] Any new north-south route is about 20 years away. I’m sure that ministers had been talking about 2025 as the potential start date. Now the Network Rail report says it will be 2030. By then I will be 55; you may well be retired or dead.

4] Funding. The Department for Transport will be squeezed, possibly harder than other departments, in the coming years. How will the route be funded?

5] In theory you could lever in some private sector funding. But NR’s report today shows that the full cost of building and running the new line (over 60 years) would be £41bn. But the extra revenue would only be £23bn. That’s an £18bn gap to fill. (There are also £31.4bn of “benefits” in the form of higher GDP due to quicker journeys)

6] NR is concerned about where to build a new station in the capital: “London itself could present an engineering, planning and affordability challenge that delays or prevents the programme being progressed.” In other words, where would you stick the new terminus? Would you have to knock down dozens of office blocks to build it?

7] Today’s announcement has been spun as some kind of Network Rail “go-ahead”. In fact, the recommendation (on page 132 of its “Strategic Business Case”) is more nuanced. It says: “The recommendation of this report is that there is a case to take the London to North West & Scotland corridor forward for further investigation.”

8] Meanwhile Andrew Adonis, transport secretary, is still claiming that high-speed rail would have environmental benefits. This is not as straightforward as it seems, however. The Guardian published a report last week showing that building the new line could produce a huge amount of emissions.