How old is English?
 I can't help myself to compare that situation with the modern position of Britain in the European Union. Many other members have the impression that Britain behaves halfhearted about Europe. The Britons want the advantages of Europe, they wish to keep their influence, but they are not prepared to give up their national currency, for instance. Are they in or out? That's the question.
411 AD (the beheading of Constantine III) is the last 'secure' date we have. The next important event is the Adventus Saxonum (when the Anglo-Saxons arrived). We don't know for sure when this happened. Many modern historians believe it happened in 428, the classic date however is 446. Between 406 (departure of Constantine III to the continent) and 428 are 21 years, between 406 and 446 are 40 years (referred to by Nennius as '40 years of fear'). It is thought that little happened during this period. Except for the continuation of the raids. The short period, or early date is therefore to be preferred. It's unlikely that the British population remained sitting ducks for 40 years. The real waiting time was in fact a bit shorter. Constantine III died in 411. Talks about making the hiring of Anglo-Saxons official started probably in 426. Thus, Britain waited for some 16 years before taking measures.
Honorius decides not to decide
What Honorius did was unprecedented: he told the British officially to defend themselves. The emperor no longer took responsibility for Britain. Defending the empire and assuring its security was the main task of the emperor. This was not quite a declaration of independence, as Britain had in theory to pay taxes. The purpose of those taxes was to pay the legions which had to defend the borders. So Britain now had to finance its own defense and had to contribute to the defense of the rest of the Empire. It would not receive protection from the Empire in return. With this declaration, the legal status of Britain became a real problem. Was Britain still a part of the Empire as the emperor himself had declared not to care any longer for the province? A possible legal interpretation, could be that Britain was no longer a part of the Empire! 
This seems harmless enough, but it wasn't. Because of that legal problem, Britain could be considered a nation foreign to the Empire. Continental local authorities now had the opportunity to subject British merchandise to (heavy) import taxes. As local politicians always are strapped for cash, it is likely that the interpretation was often applied. The people who had financed Constantine III were on the whole merchants who had hoped for more free trade, exports and profit. Trade with the Continent would now stop completely. The import taxes meant a serious price handicap. For some of Constantine's supporters, this meant ruin. Honorius had confirmed Britain's real position within the Empire: half in, half out. He punished the British traitors for supporting Constantine III. Britain had maneuvered itself in a difficult position.
Without the support of the Roman
however, the whole of the tiny British upper class
soon could have a
problem with the ‘commons’ and on top of that the
Welsh families had to
face their east-British counterparts.
The British senate must have been stunned by Honorius' decision. For centuries Britain had been a loyal part of the Empire. It's just that recently Britain had been not so loyal. It is probable that many lords (mainly in the southwest, which used to be the export region) simply couldn't accept the idea of 'independence'. Who would now legally rule Britain? A complete culture collapsed. There was confusion all over the place. Many lords already rebuffed the legality of the London senate (taxes!). Central authority crumbled. In an attempt not to worsen the situation, the senate must have decided to await Honorius' death or demise. Maybe his successor could be convinced to revoke Honorius' unfortunate decision. Conservative as always, any alternative for the Empire remained inconceivable for Britain.
That chance came in 423 when Honorius
eventual successor (Valentian III became emperor
in 425 - he was 6
years old. His mother, Galla Placidia
became the real ruler.
was supported by the emperor of the eastern Roman
was not the strong person the British had hoped for.
The return of the
Empire to Britain became doubtful.