Job offer for UK Reader I'm currently an assistant professor at a US university, three years away from coming up for tenure. Recently, a former colleague of mine who is a professor at a university in the UK approached me about joining their institution, as they were advertising a search in my area for all ranks (Lecturer-Professor). 

Even though the interview didn't go particularly well in my opinion, I just got a job offer for Reader. However, their offer would effectively require me to take a 40% salary cut. When I applied, there was a form that asked me about my current salary. After asking about this, they replied that my current salary was not taken into account as it would create a "salary anomaly" with respect to what other Readers are being paid and that the salary isn't negotiable. Note that their job ad only stated a very broad salary range (for all ranks) and hence I did not anticipate this before applying.  


Is this the usual experience when applying for academic jobs in the UK? Or, does this perhaps indicate that my application wasn't perceived to be particularly good after all?
They also stated that Reader is a "leadership position" in contrast to my current position and hence it would be a promotion. However, it's not exactly clear to me what this means in practice: Apart from the obvious advantage of not having to go through the tenure process, what other benefits does a Reader position provide over Assistant Professor?
Yes, UK salaries are currently significantly lower than US salaries at most ranks, and don't have much room for negotiation outside of a standard range.  The only exception to this is "professor" in the UK (which is often closer to distinguished professor in the US) where there's more latitude for higher salaries.

One major reason for the salary gap is that as recently as Summer 2015 the pound was worth nearly 1.6 US dollars.  If it comes back up then their offer would be more competitive, while if it goes down further then the offer will look even worse.

The only meaningful advantages I can see of a Reader over a US Assistant professor as a position is that there's more job security.  But presumably if you're a strong candidate for a Readership you shouldn't be too worried about tenure, and at many US schools this offer would get you tenure this year in a retention package.  (There are lots of advantages and disadvantages of UK vs. US which I won't get into, I'm only talking about the rank comparison.)