The constitutional expert who drew up a report for the coalition on how to tackle the impact of devolution on the status of MPs in Westminster has said his proposals will need major changes following the Scottish referendum.

Former House of Commons clerk Sir William McKay said the report he produced last year would need a "fairly hefty tweak" and could result in English MPs being given the final say on laws which only apply to their constituents.

The McKay Commission had proposed that ministers would be obliged to note whether there was an English majority for England-only legislation, but a lack of such a majority would not automatically kill the measures.

But with further devolution promised to Scotland and calls led by the Prime Minister for "English votes for English laws", Sir William acknowledged that his proposals could not be implemented without change.

It may result in having "two classes of member" at Westminster, he acknowledged.

He told BBC Radio 4's World This Weekend that in the commission's work "we recognised it was very difficult to distinguish between business in the House of Commons which referred only to England and business which referred to other bits of the UK".

He added: "We tried to avoid two classes of members - you can vote here but you can't vote there - and, finally, we said there has to be a provision for English voices but the final decision must be taken by all UK members.

"Whether, and to what extent, these have been overtaken by the result of the referendum I think is a difficult question to answer.

"But certainly you can't, I think, lower any of our solutions immediately and without amendment into the present situation. They will have to be tweaked ... A fairly hefty tweak, more of a kick than a tweak."

He added: "You would have to answer the basic question: can we still go along with the principle of not creating two sets of members? Would you need to create an English voice which was a final voice?

"You would have, perhaps, to alter drafting conventions and the way bills are framed to set out more clearly that which refers only to England. That would be very difficult, because quite often financial consequences of a bill in England have knock-on effects on the finance given in Scotland, Wales and Northern Ireland."

If extensive tax-raising powers were devolved to Holyrood, decisions on taxes could stop being issues for all UK MPs, he indicated.

"It might well," he said. "Of course it would depend on the legislation. If there are going to be two classes of decision there may have to be two classes of member."