British government officials expressed embarrassment and anger at Washington last night after they were forced to admit that US rendition flights carrying terror suspects for secret interrogation had twice landed on British soil.

In an apology to the Commons, David Miliband, the foreign secretary, told MPs that contrary to "earlier explicit assurances" two flights landed at Diego Garcia, the British Indian Ocean territory where the US has a large air base, in 2002. He said the flights had been mistakenly overlooked in previous US internal inquiries carried out at the UK's behest.

Mr Miliband denied there was a deliberate cover-up and said he believed the US had acted "in good faith". However, Gordon Brown, attending an EU summit in Brussels, expressed his "disappointment" and said Washington's failure to disclose the flights earlier was "a very serious issue".

"The US has expressed regret that it did not admit at the time to these renditions through Diego Garcia," he added. "We have to assure ourselves these procedures will never happen again."

The excuse that America didn't tell us doesn't wash

While I welcome Mr Miliband's admission and apology to the House of Commons – tardy and not entirely unsurprising though it may be – it certainly raises the question as to why it took us so long to get to this point. Liberty first wrote to the Foreign Secretary, then Jack Straw, in November 2005 expressing concern that the UK was complicit in torture flights. Rebuffed, we tried again the following year with his successor, Margaret Beckett. Once again, we were given short shrift.

So here we are, tainted by this ugly practice. It is easy to feel smug and superior about the Bush administration and, yes, its use of kidnap and torture is reprehensible in the extreme. But the "they didn't tell us!" excuse doesn't wash. Since when was our sovereign government dependent on another to keep us informed about what is happening on UK territory?

Our Government had a responsibility to investigate the allegations, a responsibility it systematically ducked. Rather than looking the other way with fingers stuck firmly in ears, there should have been a proactive and aggressive inquiry into when and why US military flights were accessing our airspace.

What should the next step be? The first must be to ensure we are never party to the shame that is extraordinary rendition ever again.

The second must be a full and proper investigation a lot closer to home. Then we can perhaps begin to forge a new "special relationship" with our cousins across the Atlantic at this historic moment in their political history.

This time, the relationship will be based on democratic values rather than our shared guilt in the grubbiest secret of the war on terror.