You can get Maternity Allowance (MA) only if you are not entitled to Statutory Maternity Pay. The ten days you mention are called Keeping In Touch (KIT) days and ANY work even for 30 minutes counts as one day. Any work done in excess of the ten days whether as self-employed or employed will affect the payment of MA.
in the legislation re the ten days it does not state what you can pay for the 10 days unless I have missed it .Presumably you can pay what you like for those ten days as long as you have not a written salary in a contract?