Black Prince was a proposed British-led satellite expendable launch system. It would have made heavy use of the preceding Blue Streak missile and the Black Knight test rocket development programmes, as well as some new elements, to produce a British-built launcher capable of deploying medium-sized payloads into orbit. Popularly known as the Black Prince due to its assigned rainbow code, in official documentation, the platform was referred to as the Blue Streak Satellite Launch Vehicle (BSSLV).

The Black Prince originated from various ballistic missile programmes that were being conducted by the United Kingdom during the 1950s. As envisioned, it was to have been a multistage rocket, the first stage being the Blue Streak and the second stage being the Black Knight. This would have been mated to a variety of different interchangeable third stages, differing based upon the individual intended mission profile. According to performance projections, the Black Prince would have been capable of delivering a 960 kg (2,117 lb) payload to a 740 km (400 nmi) orbit.

The Black Prince gained several supporters, including official government backing following the termination of military involvement in the Blue Streak programme during early 1960. It was seen as a viable means of reusing existing development work, but one that would still involve significant costs. The British government promoted the concept to other potential partners across Europe and the Commonwealth of Nations, however it became clear that the necessary backing would not be forthcoming. Work on the Black Prince launcher came to an effective halt shortly after the formation of the European Launcher Development Organisation (ELDO) working group and a government decision to proceed with British participation in the multinational Europa launcher programme instead. During the late 1960s, it was proposed that elements of the Black Knight could be combined with the later Black Arrow launcher.

During the early 1950s, the British government had identified the need to develop its own series of ballistic missiles due to advances being made in this field, particularly by the Soviet Union and the United States. A British programme to develop such a missile, named Blue Streak, was promptly initiated; however, there were key questions over the then-relatively unknown scenario of what such a vehicle would encounter when attempting re-entry to the atmosphere, there were fears that such a vehicle might simply burn up like a meteor and therefore be unachievable.

At the same time, Britain had also never previously developed a ballistic missile before, the field being relatively new and with few participants, thus there was significant value in developing and constructing a research ballistic missile in order to gain experience and data on how to design and build such vehicles, develop launch techniques, and general handling. Accordingly, during 1955, the Black Knight research rocket programme was commenced for this purpose. Following several launches, the Black Knight came to be regarded as a successful programme, having produced a relatively low cost and reliable rocket, and thus there was impetus present to proceed with further development of the platform.

The Black Prince itself has its origins in a proposed design that was put forward by Desmond King-Hele and Doreen Gilmour of the Royal Aircraft Establishment (RAE) during 1957. As envisioned by this proposal, an expendable launch system could be developed using a mix of preexisting and in-development assets; the multi-stage launcher was to be formed of a Blue Streak first stage, a Black Knight (or Black Arrow) second stage, and a military solid rocket as a third stage. The proposal, which subsequently became widely known as the Black Prince, quickly attracted the attention of a key supporter in Dr Geoffrey Pardoe, the project manager for the Blue Streak missile programme.

On 13 April 1960, the Defence Minister Harold Watkinson announced the cancellation of Blue Streak as a military programme, and went on to state that: "the Government will now consider with the firms and other interests concerned, as a matter of urgency, whether the Blue Streak programme could be adapted for the development of a launcher for space satellites." While development of the Blue Streak missile continued with the view of using it as a capable satellite launcher, the rate of work was substantially slowed. Aerospace author C.N Hill wrote that this declaration had been made: "Mainly, I suspect, to minimise the political damage that ensued from the [Blue Streak] decision".

The 1957 concept design for a combined Blue Streak-Black Knight launcher was put forward once again, and this time received a favourable appraisal; the project was assigned the rainbow code of Black Prince. In official documentation, the platform was referred to as the Blue Streak Satellite Launch Vehicle (BSSLV). The development of Black Prince was driven by the conjunction of the RAE and two private firms, aerospace manufacturer Saunders Roe and engine firm Bristol Siddeley.