'I have thoroughly enjoyed my time here,' said the 30-year-old England A cap, who joined Cardiff from Northampton in September 2001 and came on as a replacement in the Blues' loss to The Dragons on Saturday night.
'It's time for me to begin the transition from playing full-time to a professional career off the field. The part-time Bedford contract allows me to do that.'
Cardiff chief executive Robert Norster paid tribute to Allen. 'Matt has been a loyal and committed player for us,' said Norster. 'He always gives 110 percent on the field and has a mature approach off it.
'He has been as asset to the club and now the regional squad and he returns
to the East Midlands with our best wishes.'