The scheme is being piloted by the employment law team and is spearheaded by partner Elaine Aarons, who has worked a four-day week (typically cramming in 55 hours) for the past 11 years.
Flexible working will be open to all lawyers with four years' post-qualification experience as long as they are meeting their targets and clients do not suffer.
They need to come in every day, but can shave off hours at the beginning and end by working at home instead.
'You need strong personal organisation skills to earn this. It's a privilege, not a right,' says Aarons. 'You can only carry on if you continue to be as effective as before.'
The legal profession has been slow to embrace concepts like flexible working, says Aarons. Traditional employers often believe it is too woolly a concept to be workable, she added.
'This scheme is very defined and definable, perhaps because we are lawyers,' she says.
If successful, it will be rolled out throughout the firm.