In a session of "policy game-changers", public affairs expert Mark Glover said garden centres that want to extend Sunday trading need to act now to help wavering MPs to vote in favour.
Last month HW revealed that business minister Sajid Javid would make an amendment to the Enterprise Bill to force through extra Sunday hours. He expects the legislation, beginning by 25 February, to pass through Parliament to devolve to the decision on extending Sunday trading in large shops to local authorities.
Bellenden chief executive Glover said: "If you want extended Sunday trading there has never been a more important time to write to your MP about these issues."
He added that chancellor George Osborne and prime minister David Cameron both support Javid's aim to drive the competition agenda and they are all feeling confident that they have the vote in the House of Commons. He said English Votes for English Laws rules are likely to be implemented by the speaker to see off opposition from SNP MPs.
Glover suggested that the Conservatives, with Lib Dem support minus 20 "keep Sunday special" Tories, would make a 60-vote majority. However, he said the vote could be a "close thing" because the Union of Shop, Distributive & Allied Workers as well as some Conservative and Labour MPs are all against.
He said garden centres could ask staff to write to MPs and they could also lobby councils to make a decision on the issue, which would probably be decided in Parliament by the summer recess after a battle with bishops in the Lords, and would then be for councils to decide individually this autumn.
Glover said other political issues for horticulture include skills shortages, the National Living Wage, plant health, the spending review's impact on parks and climate change's impact on urban trees.
The vote on staying in Europe or taking the "Brexit" option is likely to take place on 23 June, he added, with opinions spilt on the result. In Scotland, a 5 May election could see the SNP winning every seat and Brexit may lead to another Scottish referendum. A 5 May election in Wales might see a Labour and Plaid Cymru coalition. Little change is expected in Northern Ireland. Glover said the London mayor role is "tight" between Labour and the Conservative Party.
On the National Living Wage, Glover said £7.20 per hour for over-25s from 1 April is "difficult to argue against in principle but you can argue about the speed of its introduction".