The Royal Horticultural society here recommends planting figs in a pit to restrict growth on in ground trees,I've not ready anything from folks here about doing this but was wondering if anyone does this/has tried this?-is this a peculiar English thing?.

RHS advice is as follows:

"Restrict the root run when planting figs. This will help to control the size and improve fruiting, as the fig will put more energy into fruiting instead of growth. Prepare as follows:

1, Dig a 60cm (2ft) square planting pit in the ground. For wall planting aim for the tree to be about 45cm (18ins) from the wall so the tree gets the full benefit of rain
2,Line the sides with paving slabs, allowing them to protrude 2.5-5cm (1-2in) above the level of the soil
3,Line the bottom of the pit with a 20cm (8in) layer of broken bricks, large crocks or rubble to provide good drainage, but discourage large roots growing through
4,Fill the pit with soil you dug out enriched with 10% by volume home-made compost or soil conditioner. Alternatively, refill with loam-based John Innes No 3 compost. Firm and level, make sure you leave 2.5-5cm (1-2in) watering rim.
5,Plant your tree and firm, then water in. Plant no deeper than the plant was in the original pot"

https://www.rhs.org.uk/advice/profile?PID=106

I am planning putting a row of in ground trees in my allotment this year but don't want full size fig trees so I'm wondering if this might be an effective method to achieve this,I'm probably aiming for c 6-7ft high max size(pruning to maintain size not an issue).

Anyone got any thoughts on the above method?

In the long, distant past I've heard of figs that were planted in leather briefcases, the object being to contain the roots. I have my Brown Turkey in a container roughly 2.5 ft x 1.5 x 1.5 container and it's growing beautifully.

Leather briefcase!, that's like a root 'bag' literally,lol,I suppose it would have worked for a while.I think I'm going to give it a shot,the worst that could happen is that the trees grow too beautifully and I'll have to prune them(oh no,lots of cuttings to 'dispose of').BT is one of the varieties I have lined up to go in ground, it's not a commercial BT, I don't trust them to be true as I've seen some very in-BT looking BT's for sale,its from an old tree(c100?)near me,in ground,produces beautifully every year

Yes, back in the days of Percy Thrower! lol He said there was a custom of planting fig trees in a leather briefcase. I must Google it to see if I can find out why. I have no idea why that was retained in my mind but, there it is! lol