The definition
The offshore fund rules bite on three things: a non-UK body corporate, property held on trust, and arrangements creating rights in the nature of co-ownership.
Most pooled Indian vehicles fall inside one of those descriptions.
What sits outside
A discretionary managed account is not a fund. In an Indian portfolio management service, SEBI requires that the manager must not hold client securities in its own name, so you hold the shares directly, pooled with nobody.
On that basis the offshore fund rules should not apply and your gains should be capital gains. Two honest caveats: HMRC has published no guidance on managed accounts, so this is a well-supported reading rather than settled law, and it turns on how your particular mandate is constituted.
The administrative trade
If the offshore fund rules do not apply, every trade your manager makes is your own UK disposal, each needing share-pooling treatment and a sterling conversion. Ask whether the manager provides UK-basis reporting.