This cassette release was a straight repackaging and reissue of the 1977 album 'The Very Best Of Adge Cutler'. This and the accompanying vinyl album were released in the summer of 1980 on the EMI 'Notes' record label with catalogue number TC-NTS199.
This design of cassette shell was introduced in early 1977 and was produced in both grey (as in this image) and cream coloured plastic. The text was printed directly onto the cassette body in blue (as in this image), red or black ink. As can be seen on the images the tape was produced with the Dolby noise reduction system to improve the quality of the sound when played on suitable players (noticeably to reduce the hiss associated with tape playback).
This album release appears to be only found in the grey shell with blue text.
This style of cassette case insert was introduced by EMI in early 1977. It was printed by Garrod & Lofthouse (who also produced the vinyl album sleeve) in June 1980 as indicated by the line 8006 G&L.
The insert by this time was intended to mimic the vinyl album artwork - and in this case was pretty much identical.
Beneath the catalogue number TC-NTS 199 appears another code number OC 258-06 456. Between 1969 and 1982 EMI had an international coding system which they hoped would get adopted industry wide, and they used it worldwide for their own releases. In fact, the numbers used formed the basis of the 7-digit numbers adopted in 1983 and inserted into EAN/UPC barcode-based cataloguing, used to this day