There's several schools of thought about how this ever happened:
1. Someone thought of the punning title (maybe while ensconced in a Queensway drinking den) and no-one else was sober enough to stop them making it.
2. The Marvel Two-In-One strips from RAMPAGE MAGAZINE had been more popular than anyone suspected.
3. Someone had tipped-off Marvel management that the animated Thing series (aired in the States as part of the misleadingly-titled collision-of-concepts FRED AND BARNEY MEET THE THING. They never did meet, the segments were separate) but, maybe, no-one warned them that Marvel had applied its typical quality-control process to licensing its characters and it bore little resemblance to the premise of the comics. Either way, the TV show never reached the UK.
4. Marvel, engaged in a dispute with WARRIOR MAGAZINE over ownership of the Marvel Man name, thought they'd stir the pot a little more by launching a comic with the same name as an existing Warrior strip.
5. Marvel wanted to test their new colour-at-a-lower-cover-price format before rolling it out to more established comics.
The weekly line-up was originally reprints of MARVEL TWO-IN-ONE (issue 92-100 of the Team-Up style US monthly anchored by The Thing), Iron Man and Captain America (an Avengers-centric line-up reminiscent of CAPTAIN AMERICA's weekly). But Cap was quickly jettisoned in favour of Power Man and Iron Fist (making it even more a replacement for the defunct RAMPAGE). That line-up, supported by the oddly out-of-place Donald Dogfly humour strip from Hunt Emerson, remained until the lead strip was hastily bundled into SPIDER-MAN after only 18 weeks.
TTIBB had a unique for mat amongst the M-UK line. It ran alternate colour and black and white spreads (which always gave the impression of watching a TV with a faulty colour control) following the same formula as contemporary issues of SPIDER-MAN, INDIANA JONES and THE SAVAGE SWORD OF CONAN but was able to shave a few pence off the cover price by sacrificing glossy covers (a throwback of sorts to the early seventies and the 1979-82 "Skinn format"). The format, perhaps because it wasn't well suited to M-UK's new licensed comics, never took off and wasn't used again.
Issues 1 and 2 came with free card-based gifts. The first issue came with a paper hat of the sort given out free at the Radio One Roadshow (the cover art shows it being red, but it was actually blue). Issue two excelled itself with the hilariously named Big Ben Banger (its like they employed Benny Hill to devise their giveaways), a new name for a familiar freebie.
The appearance of ROM in the lead strip (issues 15-16), reprinted from Marvel Two In One 99, marked the Space Knight's last UK appearance (his SECRET WARS II crossover was omitted from the British run).
In addition to the weekly, Marvel also published an album-format special in the summer of 1984. Strangely, in addition to more Two-in-One reprints (the Stonehenge-centric strip from US MTIO 33, the conclusion of a run of UK-based adventures), the special also ran original X-Men strips (from US issues 48 and 57) despite the fact Marvel's merry mutants had nothing to do with the weekly.
28 March 1984
The free gift cardboard cap.
4 April 1984
The free gift Big Ben Banger. Avert your eyes children!
11 April 1984
Machine Man would, later in 1984, become the first regular back-up strip in THE TRANSFORMERS.
18 April 1984
25 April 1984
2 May 1984
9 May 1984
16 May 1984
23 May 1984
30 May 1984
6 June 1984
13 June 1984
20 June 1984
28 June 1984
4 July 1984
11 July 1984
18 July 1984
25 July 1984
First merged issue.
THE THING IS BIG BEN
1984 SUMMER SPECIAL