"What leavers would like is a reasonable agreement that works for both sides"
Define 'reasonable'. What the Brexiteers want is not reasonable from the point of view of the EU. The EU rules and regulations were created through hard-won consensus between all member-states. You don't get to pick and choose the rules you like because that would break the EU. Breaking the EU is considered unreasonable by the remaining member states.
The EU offers a take it or leave it deal for members. There is the EEA and EFTA for those who want to opt out from the political union. Non-members get complicated trade agreements with limited benefits and obligations. Please stand in line over there and wait for your turn to negotiate a bilateral agreement.
I hope Britain can take their time to sort things out under EEA rules. Give them time to prepare proper Brexit or to change their minds.