The current payment system should be replaced with a single scheme, the suggested name for which is the "constituency management fee". It should be paid from central funds and drawn down by MPs annually (or in periodic increments). From this, MPs pay all expenses and remuneration, in accordance with what is most appropriate to the effective management of the constituency and which is acceptable to their local voters.
Thus, an MP will draw from the fund, the salary, pension payments, working and all other expenses (including normal travel), staff employment and all other expenses.
Accountability is maintained on the one hand by publishing a "business plan" setting out the "budget" and the expenditure heads, and then publishing quarterly audited accounts, with an annual report at the end of the year (or period). As to monitoring of expenses – and allowable amounts – this should be a matter between constituents and the MP, with the tax authorities as the arbiter, scrutinising expenditure as they do with other enterprises.
On the basis of current salaries, allowances, etc, the fund could be in the order of £300,000 a year, possibly "banded" by constituency zone, reflecting distances and other issues which affect individual MPs. The sum set would be a maximum, with each MP able to come in under the sum allocated.
To guard against abuse – as with Conway – there should then be a "recall" provision. Electors in a constituency should be able to raise a petition (say with 10,000 names) on which completion there should follow within a stated period a by-election, where the sitting MP is required to stand for re-election.
In terms of overall advantages, this has the benefit of insulating MPs from abusers. With each MP devising their individual schemes, with the agreement of their local electors, no other MPs are tainted if one or more MPs go off the rails. On the other hand, voters are empowered, and may well be inclined to take a greater interest in the workings of their constituencies and their MPs.
Within the broad scope of the scheme, there is and should be great scope for innovation and flexibility. Some MPs, for instance, may chose to appoint a local "advisory board" made up from the local "great and the good" to advise them on disbursement of funds. There is scope for each political party to issue "guidelines" on expenditure, which an MP may (or may not) vary according to local circumstances. Others may prefer to devise their own schemes.
Ultimately, this puts voters "in charge" as ultimate accountability rests with the electorate, where it should reside (and not with an unelected bureaucracy). This also should lead to some savings, as the administrative teams currently processing and authorising payments can be disbanded.