Astronomers using the telescope discovered the first evidence for a supermassive black hole (Sgr A*) at the centre of the Milky Way, and made the first optical observation of a gamma-ray burst.

In 1981 the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Netherlands Organization for Scientific Research, NWO) bought a 20% stake in the project, allowing the WHT to be given the go-ahead.

[note 1][1] The total cost of the telescope, including the dome and the full initial suite of instruments, was £15M (in 1984, equivalent to £61M in 2023[9]); within budget once inflation is taken into account.

[note 4] The telescope consists of a 4.20 m (165 in) f/2.5 primary mirror made by Owens-Illinois from Cervit, a zero-expansion glass-ceramic material, and ground by Grubb Parsons.

[10][2][7] The mirror blank was produced in 1969 as one of a set of four, along with those for the AAT, CFHT and Blanco telescopes, and was purchased for the WHT in 1979, ten years after it was made.

In its most usual configuration, a 1.00 m (39 in) hyperbolic secondary mirror made of Zerodur is used to form a Ritchey Chretien f/11 Cassegrain system with a 15 arcmin field of view.

[2][7][12] The mount is so smooth and finely balanced that before the drive motors were installed it was possible to move the then 160 long tons (160,000 kg) assembly by hand.

[2][7][13] A conventional up-down 6m-wide[7] shutter with wind-blind, several large vents with extractor fans for thermal control, and a 35-tonne (34-long-ton) capacity crane (used for moving the primary mirror e.g. for aluminising) are all incorporated.

Offices and administration are located an hour's drive away in Santa Cruz de La Palma, the island's capital.

Telescope time is distributed in proportion to this funding, although Spain receives an additional 20% allocation in return for use of the observatory site.

Prior to the installation of WEAVE (2020-22), ISIS and LIRIS were the workhorses of the WHT, with approximately two-thirds of all time awarded using those two instruments.

[20] In addition the WHT is a popular telescope for single-purpose visitor instruments, which in recent years have included PAUCam, GHαFaS, PNS, INTEGRAL, PLANETPOL, SAURON, FASTCAM and ULTRACAM.

Some of the more notable include the first evidence of a supermassive black hole (Sgr A*) at the centre of the Milky Way (in 1995)[22] and the first optical observation of a gamma-ray burst (GRB 970228) (in 1997).

In recent years (as of 2010[update]) this has included: The upcoming generation of extremely large telescopes (ELTs) will require sophisticated adaptive optics in order to be used to their full capability.

As of 2010[update], the European Southern Observatory's European-ELT (E-ELT) project had a programme to utilise the WHT as a test-bed for its adaptive optics system, and received several nights per year for on-sky testing.

[36] The UK's STFC (originally the major financial contributor) has gradually reduced its funding for the ING telescopes over a number of years.

[19] WEAVE will provide medium-high resolution spectroscopy in the visible (360–950 nm) range for up to 1000 simultaneous targets over a 2 degree field of view, and is currently expected to operate for several years.