I've been reading into the Nazanin Zaghari-Ratcliffe case a little.
Not sure there is much more the UK govt could actually do to secure her release tbh.
Some points of note

1) She works for Thomson Reuters Foundation, "created to advance & promote the highest standards in journalism worldwide through media training & humanitarian reporting".
https://www.trust.org/about-us/ 

2) She previously worked for BBC London, in their BBC Media Action wing.
Iran is said to "loathe" the BBC because of its Persian service.

3) She was arrested at Tehran airport on 3rd April 2016, whilst she was at the check-in desk to return home. She says she was there visiting her family with her young daughter.

4) Initially Iran's Revolutionary Court accused her of trying to overthrow the country's clerical govt.
They have since accused her husband of being a spy & claim she took part in anti-regime protests in 2009, getting involved in a 'soft toppling' plot of its leaders.

5) She received 5 years prison in September 2016, losing her final Appeal in January 2017. Iran's Supreme Court upheld her conviction in April 2017.

6) Her daughter (then 2yo), Gabriella, had her passport taken away following her mothers arrest & now lives with grandparents in Iran.
She finally had it returned a year later, but remains currently in Iran so she can visit her mother.

7) Nazanin Zaghari-Ratcliffe is one of about 40 or so dual nationals currently behind bars in Iran. Many of these appear to have potential political motivations & some have been there for quite some time.

8) Iran is deeply suspicious of & refuse to recognise dual nationals, so denies them access to consular assistance.
This limits the input of the UK in her case.
The British Ambassador has visited her though & she is said to be receiving some consular assistance.

9) Mr Ratcliffe has been quite critical of the UK govt since his wifes arrest, though he does seem to understand that Iran often use such cases to seek demands from other nations.

10) The allegations that BoJo has made the situation worse are not the 1st time Iran has tried to misuse public outcry.
They also claimed the initial media outcry was 'evidence' of her guilt.

11) Mr Ratcliffe has expressed that he feels his wifes detention is part of a wider political dispute going on inside Iran, something totally outside any UK influence/control.

12) Her family refused an initial 'shady' offer to release her for a £125,000 'ransom'.
This ransom was only 'payable' upon her release.

13) Theresa May appealed to the Iranian president to resolve the case in August 2016, though many media outlets appear to have forgotten her input (in a barrage of Labour accusations of inaction).

14) Mr Ratcliffe, in one of his many claims, blamed Trumps 'travel ban'.
He said his wife may be an unintended victim of this ban.

15) In another of his claims, Mr Ratcliffe blamed an "outstanding arms debt" (which Britain refuses to pay) from almost 40 years ago for his wifes predicament.

16) Mr Radcliffe went public with his wifes story after 36 days, against the advice of the Foreign Office.

17) Labour have been quite noisy on this subject, using it to criticise the govt.
They haven't, however, made any concrete suggestions on what *could* be done, other than blame the govt for inaction.

18) As with all of these cases, there are only so many 'calls' that can be made to Iran.
Dual Nationals are always at risk of arrest as Iran uses them to gain leverage on the rest of the world, as they have always done.
/END