The two answers, and what each one costs
<b>A retention.</b> A sum is held back from the purchase money by the solicitors until the final accounts arrive, then distributed. It is the safe answer. It carries a fee, because accounts are often not finalised for a long time after completion and somebody has to correspond with the landlord, the agent and both sets of solicitors until they are.
<b>A clean break.</b> Nothing is held back. You take the risk of an excess charge and you take the benefit if the charges come in under budget. No fee, no loose end, no months of correspondence.
<b>A clean break allowance.</b> The middle answer: no retention, but the seller gives you a sum on completion against the estimated excess. It settles the money at the table.
How to decide
The question is the history. Where the accounts show no pattern of excess charges and the managing agent reports no unusual works, a clean break is usually the proportionate answer. Where there is a history of excesses, or works are in prospect, the retention — or an allowance measured against it — is there for a reason.
Ask for the last three years of service charge accounts and ask the agent directly whether anything unusual is pending. Both are routine requests, and they turn the decision into arithmetic rather than instinct.
Separately from all of this, the ordinary apportionment of service charge and ground rent happens on completion in any event, and cannot be calculated until a completion date is agreed.