I have got (and had) several SMLE's and No4 LE's in 410 but have yet to find any magazine that works with them hence, are they not, by default 'single shot' ?
Most of the ones I have seen have a wooden 'blanking plate', in place of the magazine and it is then used as a 'loading ramp'.
The last No4 (410) I bought had a thin steel plate shaped & held in place by the trigger guard.
The nearest I got to a working magazine was to fit (trial & error, and then 'resin' into place) a Saiga 410 magazine into the Enfield magazine (a la No7 and the BSA .22 mag)
It worked fairly well but not consistently.