There's something strangely familiar about Slaughter and May's latest role on a hostile takeover.

It emerged late last week the magic circle firm was advising NSF on an unsolicited offer for Provident Financial. Crucially, Provident is a former client.

For those who have been in the profession a while, this might trigger memories of when Freshfields Bruckhaus Deringer started advising Philip Green on a hostile bid for Marks & Spencer in 2004.

The story became the stuff of City legend when Slaughters, advising M&S, managed to get Freshfields thrown off the case due to the inherent conflicts at play. The takeover attempt ultimately failed and Slaughters was heralded for its ability to pull off such a masterstroke.

Could something similar happen this time around with Slaughters on the receiving end?

Partners at rival firms say the Provident Financial bid is a different situation to the M&S one. Clifford Chance is advising Provident, and a person with knowledge of the deal said the firm was unlikely to pursue the conflict of interest point, given that the relationship between Slaughters and Provident is historic – about five years out of date.  

Presumably, Slaughters is also confident its previous advice for the company will not cause any problems. Given it devised the 'conflict' argument against Freshfields all those years ago, it should be pretty well prepared to ensure it doesn't fall prey to its own tactic.

But it does also feel strange that Slaughters would find itself in a similar situation to the one it so effectively fought against.

There are no rules against acting against a former client. But there are inevitable risks. One partner at a rival City firm said the key issue is whether the firm in question holds confidential information that is material to the current transaction.

In other words, could Slaughters know something about Provident that is relevant to the deal and not accessible to the public?

This seems to be where the Provident situation differs from the M&S debacle. For one person close to Slaughters, it is "clear cut". What blew it for Freshfields back in 2004, they said, was that the firm was still acting for M&S while also acting for Green. It was busily renegotiating a joint venture deal, on behalf of the retail giant, for the Per Una clothing line.

Slaughters successfully injuncted its magic circle rival due to the risk that it held confidential information relevant to Green's bid that it was deemed had not been effectively walled off.

One City partner said: "Working historically with a client is not a bar to working on the other side. But hostile takeovers are rare and you need to be alive to the risks. You don't want to be in a position where the adviser becomes the problem, do you? And [for the Provident deal] it's bloody unlikely Slaughters won't have considered everything it needs to."

So don't expect an effort to throw Slaughters off the deal. But don't expect the process to be all kind and gentlemanly either. This morning, via a London Stock Exchange announcement, Provident's bosses described the proposed hostile takeover offer as "irresponsible", believing the move could have a "destabilising impact" on customers and shareholders.

In rebuffing the bid, Provident's chairman, Patrick Snowball, said his management team was going to do "everything it can" to maximise value for all shareholders during the coming weeks and "will explore all appropriate alternatives to achieve that objective".

And a twist in the tale could arise in a different way. One person said there's a chance that, Barry O'Brien, the former Freshfields partner who was at the centre of the M&S storm – the man who suffered an extensive regulatory investigation and had to pay a fine – might also end up getting involved in the Provident deal through his role at Jefferies.

That would be both bizarre and surprising, even for Slaughters.