Very unlikely that the real broadcast will resurface.

Early less successful VCR cassette formats and recorders did exist between 1971 and 1977 (the latter year of this TV hijacking) in the form of Sony's U-matic, Cartrivision, Philips' VCR (Video Cassette Recording), Sanyo's V-Cord, Matsushita's VX, Akai's VK, and of course the late introductions of both Sony's BetaMax and JVC's VHS (Video Home System).

However, the only less successful formats that were available in 1977 the UK at the time were Sony's U-matic and Philips' VCR (Video Cassette Recording), as Sony's BetaMax and JVC's VHS formats were only about to be released somewhere between mid to late 1977 or early to mid 1978 depending on your source, and even if a viewer's off-air recording did exist on either of these less successful VCR recording formats, the tape of either format it would've been recorded on would've been too damaged to get repaired.