Found a paper just now.
Lots of juicy stuff:
This article goes on to give three reasons for why the Wilson government might not have wanted to let the U.N. handle things. Anyway I think it's worth a skim and I'm not going to quote it all verbatim, but really provides more meat for this discussion.
Chapter Two
Alternatives: The United Nations, and the Use of Force
[...]
The Government’s reluctance to hand over the problem to the United Nations is worth examining, because it saddled Britain with primary responsibility for Rhodesia until it obtained its legal independence as Zimbabwe in 1980. This chapter will argue that the most significant reason why the British Government sought to maintain control of the Rhodesian problem at the United Nations is that it was desperate to avoid creating a precedent for UN sanctions against South Africa, which would be highly damaging to the British economy. Another key issue at the time, which has remained controversial ever since, is whether the Wilson Government could, or should, have used force against Ian Smith’s regime in order to prevent UDI or, after it had occurred, to compel Rhodesia to walk a legal path to independence. Michael Stewart, Secretary of State for Foreign Affairs (1965-1966) wrote in his memoirs that military intervention would have been too risky: ‘All the evidence before us was to the effect that [Rhodesia’s] forces were well-armed and well-trained; and that they would fight. This would not be a colonial expedition but a medium-sized war of uncertain duration.’ On the other hand, James Callaghan, Chancellor of the Exchequer (1964-1967), recognised in retrospect that a more coercive strategy might have yielded beneficial results: ‘I do not disguise my regret nor my belief that more forceful action by us at the time might have saved Britain from many uncomfortable moments in later years.’ This chapter demonstrates that the British Government rejected the option of using force because it was engaged in a desperate struggle to limit its military liabilities for economic reasons. These were the chief concerns guiding the Government’s calculations, but publicly it was prudent to argue that the use of force was neither militarily feasible, nor desirable because of popular sympathy for Rhodesian ‘kith and kin’. However, it will be argued below that even though the circumstances were not particularly favourable to military intervention, the ‘more forceful action’ advocated by Callaghan was practicable and likely to have succeeded.
Lots of juicy stuff:
In November 1964, a British Cabinet sub-committee considered a list of proposals for the solution of the Rhodesian problem, which Arthur Bottomley presented ‘roughly in ascending order of acceptability to Mr Smith’:
1. Hand over to the UN, admitting that the UK has no solution to the problem (similar to Palestine).
2. Suspend the Rhodesian Constitution and impose direct rule by force.
3. Amend the current Constitution to enfranchise the Africans.
4. Summon an immediate Constitutional conference in London or Salisbury.
5. Allow independence on the basis of the 1961 Constitution, provided that the Africans are enfranchised beforehand.
6. Persuade Smith to accept a Commonwealth Commission to try to devise a solution to the problem.
7. [Her Majesty’s Government] to devise a new Constitution with a bicameral legislature, the second chamber of which would contain an African majority.
8. Ask Smith to provide greater evidence of Rhodesian support for independence on the basis of the 1961 Constitution.
9. Suggest a national meeting similar to the ‘National Convention’ held under the governorship of Sir J. Kennedy in 1960.
10. Suggest a political moratorium on the independence issue, with the UK or Commonwealth intervening to dissuade the African Nationalists from unconstitutional action.
11. Persuade Smith to make a concession to the African Nationalists by incorporating a few of them into his Government.
12. Propose that the convention of non-intervention in Rhodesian affairs by the British Parliament be formalised, but with [Her Majesty’s Government] retaining responsibility for external affairs.
13. Grant immediate independence with safeguards against repeal of the entrenched clauses of the Constitution.
14. Grant unconditional independence.
Officials in the Foreign Office West and Central Africa Department later suggested: ‘This is a threat to which precisely the most reactionary and stubborn Rhodesians would be likely to be most susceptible.’ It was argued that handing over the problem to the United Nations would have several advantages: it would accept the facts of the situation (namely that the British Government had no ability to control the situation in Rhodesia); it would obviate the need for a general trade embargo; and it would demonstrate that British policy was not motivated by favouritism towards the white minority in Rhodesia. It also became apparent shortly before UDI that a majority of the British public (some 63 per cent) was in favour of handing responsibility for Rhodesia to the United Nations.
This article goes on to give three reasons for why the Wilson government might not have wanted to let the U.N. handle things. Anyway I think it's worth a skim and I'm not going to quote it all verbatim, but really provides more meat for this discussion.