Can you please explain to me whether the Contractor owns float under the ECC form of contract?
There are other similar questions that have been asked within this platform and it will be worth you looking at those similar questions, but to answer it briefly here:
It depends what float you are talking about. Total Float, which is the amount that non-critical path activities can slip without affecting the critical path is shared. It can be used by the Contractor to absorb delays or rescheduling, but equally can be used by the Employer when assessing compensation events. If a compensation event delays an activity by one week and has two weeks total float, then there will be no affect on the Completion Date/Key Date. This is summarised in clause 63.3.
Time risk allowances which is in effect another type of float is owned by the Contractor as these are for items that are their risk under the contract. These can not be used to absorb the effects of compensation events.
Lastly, terminal float which is when planned Completion is in advance of Completion Date is owned again by the Contractor. If there is a compensation event that delays planned Completion by one week, and planned Completion was already two weeks earlier than Completion Date on the last Accepted Programme, then both planned Completion and Completion Date will both move by a week (once the compensation event is implemented). This is again explained very clearly in the guidance notes for clause 63.3.