I wouldn't swear to it, but I think they actually voted in favour of agreeing to set a rate, but not actually setting it, iyswim
Turns out there is a huge article in Wikipedia about the Ratecapping Rebellion - dealing with the whole country.
The detail on Lambeth is here:
Lambeth[edit]
From the start, Lambeth had been in the forefront of the campaign. Despite rumours that three might break ranks, all 34 Labour councillors present voted on 7 March 1985 not to set a rate.
[190] As the new financial year approached, Labour councillor Stewart Cakebread dissented, saying that a budget set at the cap limit would not require cuts.
[191] The Conservative group summoned an emergency meeting on 10 April 1985 but their proposal for a legal rate was defeated by 34 to 30.
[192] A second Labour councillor, Janet Boston, rebelled at a special policy committee meeting on 30 April, supporting a Conservative motion to call a special council meeting on Sunday 5 May; both Boston and Cakebread were
barristers. Meanwhile, council officials estimated that the failure to set a rate by 1 May had already cost the council £170,000 in lost interest.
[193]
As had happened on other councils, the district auditor wrote to all councillors on 9 May telling them that an extraordinary audit would follow if no rate had been set by the end of the month; council leader
Ted Knight insisted that the council would not set a rate at its meeting on 15 May "or any time after until the Government returns the money it has taken from us".
[154]At this meeting a third Labour councillor, Vince Leon, joined Boston and Cakebread in voting for legal budgets.
[194] Boston and Cakebread were removed from all committees by the Lambeth Labour Group at the end of the month,
[195] and Boston was told to resign her seat by her local ward Labour Party (she refused). Cakebread received the support of his branch.
[196]
Lambeth town hall, a focus for the council's protests and also where territory was recaptured from the Auditor.
The district auditor, Brian Skinner, found that his permission to use offices in Lambeth town hall allocated to
NALGO was withdrawn in mid-May;
[197] he was also surprised to discover his photograph on a threatening mock
'Wanted' poster in his local supermarket. Skinner's employers, the
Audit Commission, sought police assistance in tracking down and destroying copies of the poster.
[198] After a council meeting on 5 June again rejected a legal budget (by 32–30), the Audit Commission stated that a letter would be sent immediately to all councillors who had not voted for the motion (possibly including two Conservatives who had been absent) notifying them of an extraordinary audit and possible surcharge over lost interest which by then amounted to over £270,000.
[199]
While the council finances were sustained by loans amounting to £29m from the
Public Works Loan Board,
[200] the resignation of Labour councillor Mike Bright on 21 June 1985 put those supporting continued defiance in the minority. Bright wrote a resignation letter revealing he saw no hope of success and expected to be surcharged: "Martyrdom, however heroic, is usually the sign of a lost cause".
[201] Ted Knight described Bright as a "victim of [the state] machine".
[202] After a formal notice of an extraordinary audit was published on 18 June,
[203] 32 councillors received notice on 27 June that the auditor deemed them liable to a surcharge of £126,947.
[204] The response of the councillors was to set up a 'Fighting Fund' in their defence, which was supported at its launch by the prominent actors
Jill Gascoine,
Frances de la Tour,
Matthew Kelly, and
Timothy West;
[205]the Labour group debated whether Mike Bright ought to be eligible for help from the fund.
[204]
At the next council meeting on 3 July, there was uproar after members of
Vauxhall Constituency Labour Party unfurled a banner from the public gallery behind the Conservative group. When Conservative councillor Tony Green tore the banner down, Labour councillor Terry Rich rushed across to confront him and was only held back in a headlock by another councillor. The meeting was adjourned for 20 minutes. When it resumed, Janet Boston and Stuart Cakebread moved a legal rate which was passed by 32 to 31.
[206] The council was able to avoid cuts in planned spending with the aid of additional £5.5m housing subsidy from the Government and £6m from the Greater London Council's 'stress boroughs' scheme,
[207] the Lambeth Fighting Fund therefore claimed the campaign had been a success "in financial terms".
[208]
As you can see this article is annotated, so I guess post corona we could saunter off to the Minet Library archives and read the bits of the South London Press.
To come back to my question - and your answer - it seems Cllrs Janet Boston and Stuart Cakebread proposed a legal rate, which was then voted through by them and the opposition (who were probably 27 Tory & 3 SDP/Liberal Alliance at a guess).
