Top Gear's executive producer, Andy Wilman, has expressed regret for offence caused by a remark on the show made by presenter Jeremy Clarkson that some viewers found racist.

Wilman's statement was made following a formal complaint about the BBC2 motoring show's Burma special broadcast in March. During the programme, Clarkson and co-hosts Richard Hammond and James May built a bridge over the River Kwai in Thailand.

As an Asian man was seen walking along the bridge, Clarkson said: "That is a proud moment, but there's a slope on it." Hammond replied: "You're right, it's definitely higher on that side."

Actor Somi Guha who has appeared in former ITV drama The Bill instructed lawyers to complain about Clarkson's use of the word "slope".

The law firm Equal Justice claimed it contravened the Equality Act 2010 as it can be used as a derogatory term for people of Asian descent and threatened to take the issue to regulator Ofcom and consider legal action.

In a statement, Wilman said: "When we used the word "slope" in the recent Top Gear Burma special it was a light-hearted wordplay joke referencing both the build quality of the bridge and the local Asian man who was crossing it.

"We were not aware at the time, and it has subsequently been brought to our attention, that the word 'slope' is considered by some to be offensive and although it might not be widely recognised in the UK, we appreciate that it can be considered offensive to some here and overseas, for example in Australia and the USA.

He added: "If we had known that at the time we would not have broadcast the word in this context and regret any offence caused."

Wilman's comments did not address the other concerns raised in the letter sent on behalf of Guha which called for Top Gear to "be censured to ensure that another race or nation is not targeted", and asked that the BBC should give "due consideration to not re-commissioning Top Gear until these matters are addressed".

In the formal complaint, which was also sent to the BBC Trust, law firm Equal Justice wrote: "Casual racism in the media by established BBC stalwarts is constantly brushed aside."

It is not the first time Top Gear has apologised over remarks made about other nationalities.

In February 2011, it issued an apology after Hammond made a joke about Mexican cars reflecting Mexican stereotypes who were, "just going to be lazy, feckless, flatulent, overweight, leaning against a fence asleep looking at a cactus with a blanket with a hole in the middle on as a coat".

The BBC declined to comment further.