Herbert Smith Freehills (HSF), DLA Piper and Allen & Overy (A&O) have the lowest proportion of partners over the age of 50, according to a Legal Week research project into the ages of partners at the UK's ten largest firms by revenue.

Both HSF and the international limited liability partnership (LLP) of DLA Piper have just 22% of partners aged 51 and above, compared to a group-wide average of 27%.

The figure is 23% for A&O, thought the number of partners at the magic circle firm aged 56 or higher drops to 7%, the joint lowest proportion of all firms surveyed.

Conversely, Freshfields Bruckhaus Deringer has by far the largest proportion of its partners in the 51-plus category, with 35%, while 13% of its partners are aged 56 or more.

At the other end of the spectrum, HSF also has the highest proportion of partners aged 40 and under, with 27% of the members listed on the firm's returns on Companies House in the age category, and a full five per cent of the partnership aged 35 or below.

At 30 years old, HSF also has the youngest partner of any firm surveyed.

The data was collected from each the returns each firm must file at least once a year on Companies' House, which comprises the majority of partners at each LLP, excepting partners and offices omitted from the list of members for tax reasons or different year-ends.

As such, the data – a full analysis of which can be found here – cannot be taken as an exhaustive survey of all partners, even though the sample size accounts for around 80% of all partners.

For Hogan Lovells, DLA Piper and Norton Rose, the LLP filings only account for the international or UK arms of the partnership, while Slaughter and May is omitted from the group, as it is not structured as an LLP.