A voluntary termination is a flag that will appear next to the account on your credit file (not in the payment history). This is not a problem, it simply tells any potential lender (though I doubt many if any would look too closely at a VT) what you did, you voluntarily terminated the agreement. This is NOT (and won't be seen as) adverse as it is done under the terms of the agreement.
Be cautious though, as sometimes HP agreements terminated like this are recorded (wrongly) as a voluntary repossession. This would appear in the payment history and would be treated as adverse.
If you do return a HP car under the terms of the agreement do check shortly afterwards (allowing 30ish days for the account to be updated on your credit file) that it has been registered as a Settled (Voluntary Termination) and not a Voluntary Repossession. If it has been registered wrongly contact the finance provider and the Credit Reference Agency (or probably all three!).