The glottal stop found in Cockney and in many Estuary English speakers ("sa'elli'e dish" and "Conserva'ive par'y" for "satellite dish" and "Conservative party") is a feature belonging to these particular accents, and is not a result of sloppy speech.
Wherever the glottal stop occurs - whether in Estuary English territory or in Glasgow - it is disdained by many members of the middle and upper classes. I have found Estuary English referred to as "slobspeak" (Edward Pearce in the Guardian) and "slack-mouthed patois" (Keith Waterhouse in the Daily Mail).
While attacking people on grounds of race, sex or age is considered politically incorrect, it is still surprisingly common to encounter attacks based on accent, especially if those accents originate in the lower classes.
In theory, it ought to be possible to convince fair-minded people that all accents are equally valid, as long as they are mutually intelligible.
However, since I and many other linguists have over the past two or three decades failed miserably in our efforts to convince, I have come to the conclusion that we should introduce into our schools "language awareness programmes" which cover not only the features of Received Pronunciation and local accents, but also the common reactions which the more stigmatised varieties evoke.
If a pupil is going to make a good impression in a job interview in which people like Mrs Shephard are on the panel, then she should be aware that the use of the glottal stop, popular though it is with the youth of today, will mean failure to get the job.
School of European and Modern Language Studies
University of Kent.