I'll come up with something ...

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Note added at 3 hrs (2010-04-27 13:59:28 GMT)
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This will ensure straight perpendicular joints up the roof. Every tile/slate on the curved section of roof will need to be cut. The amount of TAPER in the ...
www.roofconsult.co.uk › Articles › Slating & Tiling Tips

Swept valley
A swept valley is a valley formed of TAPERED TILES nailed to a support board that bridges the junction of two roof slopes at an inclined valley [ ... ]
As the tiles progress around the valley on each course from one roof slope to the other, the tiles must be CUT TO A TAPER TO FIT. TAPERING THE TILES makes the tiles at the leading edge narrower and the perp joints should be maintained on the curve and lost in the adjacent roof slope. Each tile joint on the curve should fall in the centre of the tile below to give the maximum side lap with the joint on the course below. This is best achieved by setting out the valley from the centre line and working out onto each adjacent roof slope. BS5534 requires a minimum side lap of 55mm.
As the TILES ARE CUT TO A TAPER and work progresses up the roof, the side lap will increase to the point where a tile is not wide enough and a tile-and-a half is needed
http://www.roofconsult.co.uk/articles/tiling/tips37.htm

The roof tiles are notable because they had to be hand-made in over a dozen different shapes and sizes to follow the TAPERING, S-curved roof shape. ...
www.heritagearchitecture.com/projects/reconstruction/aksmil... (applies to the roof, not to the tiles, but possibly the same result could have been achieved by tapering tiles (if they could be cut); otherwise, the "dozen different shapes" may well have included special tapered tiles)

Curved Roofs
Single lap slates do not like going around any form of curve. Some can be made to do so, but in most instances it will reduce performance to rain penetration. This may result in a steeper rafter pitch being required. The ability of double lap slates to be TAPERED TO FIT and available in a wide variety of sizes makes them more ideal for curved roofs. [ .. ] Also on a large radius the shunt in the interlocks may allow a little TAPERING, as the radius gets smaller the slates will become impossible to lay without damaging or compromising the interlocks. Slates, being flat, will form a tangent to the curve and produce triangular gaps under the slates that will get bigger with wider slates and on tighter curves.
http://www.roofconsult.co.uk/articles/tiling/tips9.htm

7 OAST TAPER TILES and vertical tile-hanging
http://www.spab.org.uk/on-line-shop/new-publications/
Ah, yes, oast houses probably require tapered tiles. Must ask cousin Phil of Oast Farm, near Buxted (if anyone local is looking for a nice farm shop ...)

welcome to tudor roof tiles - manufacturers and distributers of roof tile, hand made clay rooftiles, creasing tiles, peg tiles, OAST TILES, TAPERED TILES.
www.tudorrooftiles.co.uk/?content=company

Aldershaw Handmade Tile Ltd make a number of tradtional clay products, and use the local Wealden clay. Products include handmade peg tiles, Cambridge mix tiles, oast house tiles, ornamental tiles, roof finials , floor tiles and mathematical tiles.
http://www.theheritagedirectory.co.uk/product.asp?prodid=200

and many are available in special sizes, including the old 'Kent Peg' size, TAPERED OAST TILES, ornamental tiles, and mathematical tiles. ...
www.ashford.gov.uk › ... › Listed Buildings

I guess interlocking tiles have to be specially made for each project since cutting and tapering would not make interlocking possible:
With MCA’s Turret Tile, clay turret tiles are custom-made for each job to specification. The tile is graduated, with larger tiles at the bottom, medium tiles in the center, and small, TAPERED TILES at the top. The exact number of each size of turret tile is calculated using computer design. The tiles are made to fit the specific turret, in the color specified. The hand cutting and waste are eliminated.
http://www.mca-tile.com/articleAW11_07.htm

our national heritage In addition, we also produce traditional Kent peg tiles, eaves, gables and TAPERED TILES FOR ROUNDELS ON OAST HOUSES or … ...
www.hotfroguk.co.uk/Products/ceramic-tiles/Ken