The VC10 had a T tail so that the engines could be mounted at the back. The main reason was that it was designed for the British ''Empire Routes'' which had short and high runways. Having the engines at the back meant the whole length of the wing could be used for high lift devices. Consequently had much slower take off and landing speeds that it's competitor, the B707. IIRC, the approach speed was some 20 to 25 konts slower for similar weights.
However, the extra structure of the suppot for the engines being away from the lift generators (the wings) added some seven tonnes to the structure and the VC10 was quite a bit heavier and more expensive to build than the B707 - one of the reasons it wasn't a huge commercial success and why only about 60 were built.
Incidently, Boeing got round the problem of the 707's inferior performance by getting the US Government to fund longer runways at all of it's destinations!