Britain gave details Thursday of major army cuts which will see it lose 20,000 regular soldiers by 2020, taking force levels to their lowest since the early 19th century.

Defence Secretary Philip Hammond told the House of Commons that 17 major units would be axed as part of an overall reduction from 102,000 regular troops to 82,000.

The cuts come as Britain battles to impose budget savings across the board in a troubled economic climate.

"After inheriting a massive overspend from the last government, we have had to make tough decisions to implement our vision of a formidable, adaptable and flexible armed forces," Hammond said.

"After a decade of enduring operations, we need to transform the army and build a balanced, capable and adaptable force ready to face the future."

Four infantry battalions are among those which will be scrapped while a fifth will be reduced to carrying out public duties only.

The changes will also see Britain become more reliant on part-time soldiers, with the number of reservists expected to double to 30,000. That will give a combined force size of 120,000.

The extent of the cuts has been known for a year but the decision to axe famous battalions of the British army has provoked sharp criticism.

The BBC reported that they will leave the regular army around half the size it was during the Cold War era -- in 1978, it was 163,000 strong.

Brigadier David Paterson has written to General Peter Wall, the chief of the General Staff, to say that he is "bitterly disappointed" by proposals to axe some of the country's most celebrated battalions, the Daily Telegraph reported Tuesday.

"It cannot be presented as the best or most sensible military option," wrote Paterson, the honorary Colonel of the Royal Regiment of Fusiliers.

Richard Dannatt, a former head of the army, told BBC radio that the cuts would entail "some risks."

"It (the army) won't be capable of conducting two operations simultaneously of the scale of Iraq and Afghanistan as we have done over the last 10 years," he said.

"It will mean that we can do less but we will still do an enormous amount."

Britain currently has around 9,500 troops serving as part of the international force in Afghanistan.

But Wall defended the plan, saying it would allow the army to become "better integrated and fully adaptable".

"The changes... will demand resilience, flexibility and genuine adaptability from our talented and committed officers and soldiers," he said.

"It is inevitable that some units will be lost or will merge but we have done this in a way that I believe is fair across the whole army."