Yes, you can negotiate your salary …
I, and several of my friends, successfully negotiated an increased initial postdoc salary in the UK.
… but it’s hard
First off, the timing is awkward: It’s altogether common to start your postdoc work without a contract in hand. At this point your chance for negotiation is effectively over (or at least greatly diminished). Many postdocs even start without having formally defended their PhD, which makes negotiation even harder (because your previous salary is very low, and you don’t yet have the degree, which determines the salary).
In addition, there isn’t a good time during the interview to bring up the salary. This is also true in industry but it’s even harder in postdoc interviews: depending on the circumstances there might not even be a formal interview.1 My advice is to bring it up before you commit, even hypothetically, to starting the postdoc. This may seem obvious but it’s not.
Secondly, you are negotiating with two distinct parties: your prospective group leader, who will also be your line manager, as well as the University’s HR department.
In my experience, your future PI is probably happy to support your demands, if they’re at all interested in hiring you. In fact, if the PI is blocking the salary negotiation I’d count that as a major red flag.
The University HR department, on the other hand, aims to keep cost low. They want you to justify every single increase. I had it easy, I was able to provide a salary statement from my previous “bridging postdoc”, which happened to be outrageously high by UK standards.2 Prepare to provide an extensive record of your work experience prior to, during and after your PhD. This seems to be the single most relevant argument for an increased starting salary scale point.
The easiest way of increasing your starting salary would be to get hired as a senior postdoc. But this effectively requires either extensive previous postdoctoral experience (which you don’t seem to have), or the support of your former PI; and your future line manager will still need to provide compelling reasons to HR.
You should negotiate your salary
Universities don’t really expect postdocs to negotiate their salaries. They expect them to accept whatever offer lands on their table. Some institutes3 go to great lengths to avoid having to negotiate, for instance by billing the postdoc as a “postdoctoral trainee”, rather than a full fellowship or research position, or by refusing to acknowledge relevant work experience before the completion of the PhD.4
I find this unacceptable, and strongly recommend pushing back. Prepare to walk away from an offer that refuses to acknowledge your work experience in a salary negotiation, or which pretend that you’re still a “trainee” after ten years5 of University education. This isn’t being “materially minded”, it’s valuing your own worth. Postdoctoral salaries in the UK are low enough as it is, compared to cost of living. Other European countries pay a lot more.
In sum, I strongly advise everybody looking for a postdoc to negotiate their starting salary.
1 For the position that I ended up accepting, I didn’t have a formal interview: I met the PI pre-interview and then scheduled a separate day to present my research to his group, and talk to its members, without the PI present at any point. After that I got a formal offer by letter. Luckily I had already mentioned the salary to the PI beforehand. So when I received the offer which put me into the minimum salary point, I replied to HR (CC’ing the PI) with my demands.
2 I did the bridging postdoc in the UK but working for an international organisation so I was paid a salary that’s competitive internationally, which the UK postdoc salary is decidedly not (my bridging postdoc salary was ~ 38k GBP; for comparison, the starting postdoc salary at the University of Cambridge was ~ 29k GBP at the time).
3 E.g. the Francis Crick Institute in London. Shame on them.
4 Even if you have several years’ worth of relevant work experience pre-PhD, the Crick Institute’s internal rules ignore this for the purpose of salary calculations.
5 Assuming undergrad, master & PhD.