I can't add much more than I mentioned on the other forum, in that these shooting kits were sold by catalogues such as John Moores during the 1960s and early 1970s. I had a Webley Falcon pack for a while and Junior air pistol kits are also known.
The kit provided all that was needed for the lucky recipient to go shooting as soon as the parcel was opened, namely pellets, targets and target holder. Oil was included to keep the pistol maintained over time and this is the only Premier set I have come across. The Falcon I once owned was the only such Falcon I kit had ever come across too, so neither are common.
I haven't seen reference to the shooting kits in 1967 and 1971 Webley catalogues and this is the period I'd estimate the kit dates from. However, if anyone has a John Moore or similar catalogue from this time period, it may be worth checking to see if such a kit was offered and maybe even pictured.
As to value, this is a unique item and one that many a Webley collector (including myself) would like to own, so it is hard to estimate a hard price.
The Webley Falcon pack I owned sold for £395, which is almost bang on the £400 value others have estimated. Another unique Premier kit is the one offered with an attache style pistol case from C.1970 and the one pictured sold for £350 a few Kemptons ago.

I'm sure many would pay in excess of £400 if this was offered for sale and no, that's not an offer from me!
John
Currently looking for Baikal Makarov pistols with the following prefixes to the serial number: 98, T01,
Prefer boxed or cased but will consider loose examples too.