As the inventor of Road Equivalent Tariff (RET) some 30 years ago, I am delighted that at last there is to be a two-and-a-half-year pilot of RET in the Western Isles. I must, however, challenge the absurd assertion by LibDem MSP Tavish Scott that this innovation is "blatant discrimination" against Orkney and Shetland. This claim is quite unfounded and I need to put the record straight.

The Western Isles Council (Comhairle nan Eilean Siar) has, over the past five years, on a cross-party basis, undertaken in-depth research into ferry fares and, in particular, RET. It should be noted that none of the local authorities of Shetland, Orkney or, indeed, Argyll and Bute expressed any interest in participating in this work. This research offered the Scottish Government a ready-made basis on which to mount its £22.5m trial. Two and a half years is the minimum time in which resulting traffic trends and economic impacts can be evaluated.

The most astonishing thing about Tavish Scott's claim, however, is that Orkney and Shetland are somehow disadvantaged by this. In fact, the three NorthLink Orkney and Shetland ferry services are by far the most heavily subsidised in the UK at £31m per annum. Even the high-season vehicle fare between Aberdeen and Shetland, for example, is below RET level on the 200-mile plus passage. In the case of Orkney the excellent Pentland Ferries service between St Margaret's Hope (Orkney) and Gills Bay (Caithness), developed by Orkney businessman Andrew Banks, provides an inexpensive, popular and frequent service without one penny of public funding.

Contrary to Tavish Scott's claim, it is Orkney and Shetland that have hitherto had an unfair advantage of cheap fares and massive subsidy. Rather than make wild accusations, unsubstantiated by fact, Mr Scott should withdraw his assertion and welcome the Scottish Government's well-conceived initiative to enable the Western Isles to catch up.

Roy N Pedersen, SNP Councillor, 8 Drummond Road, Inverness.

The long-overdue Road Equivalent Tariff pilot study for our island ferry services is to be welcomed, and despite the by now habitual spitting out of the dummy by the LibDems, it is absolutely right that the pilot scheme should take place in the Western Isles, whose communities have seen none of the massive benefits that have accrued to Shetland and, to a somewhat lesser extent, Orkney, through nearly four decades of flowing oil.

There may be a little welcome levity to come from all of this. Will, for instance, the tariff be calculated in "nautical" or in "statute" miles? Perhaps more importantly, how many of our civil servants or politicians actually know there is a difference? (Neither has any effect on air miles, although an air mile is, in fact, a nautical mile, which, as an added bonus to collectors, is longer than an ordinary mile).

The answers to these important questions are unlikely to affect the price of mince or cabbages in Castlebay or Boisdale. RET most certainly will.

Niall McKillop, Ford Cottage, Badabrie, Banavie, Fort William.