Opening savings account with someone separated from partner but not legally

This is about deposits but bit legal too so thought this place best.

Colleague is seeing someone nearly 2 years who was married, but is separated for 6yrs - but not legally(mediation agreement only).
They are interested in setting up join account for their future together but are unsure as to any implications to the account once legalities come into play with his partner and her ex.
Are they as well to keep things separate themselves or have savings in his name only.
any advice welcome. His partner has not seen a solicitor re separating.

Why on earth would they want to complicate things with a savings account like this?

If they are living together and have joint expenses, they can open a joint current account to pay their expenses.

We will call your colleague John.
We will call his girlfriend Mary
We will call her ex, X.

Mary will have to declare her assets in any legal separation or divorce. There may well be an investigation into the source of them. Were they Mary's or John's. Was she just trying to put her assets into John's name?

If John dies, the joint account will become Mary's.

If Mary dies, the joint account will become John's.

But she can probably achieve this by getting legally separated and doing a will.

There is no harm in getting informal views and ideas here, but she should consult her solicitor before opening any account with John.

Brendan