In general bail is a right unless it can be shown that, if released, the defendant is likely to:
1. Abscond (i.e. not turn up for his next hearing)
2. Interfere with the course of justice (particularly witnesses)
3. Commit further offences.
If bail has already been granted it is very unusual for it to be withdrawn unless the defendant changes his behaviour and leads the court to believe he might do one of the above.
Sureties and securities (the promise or deposit of money) are seldom used in UK courts to secure bail.