(... with considerable thanks to Guy Taylor, and his copy of Archbold)
This is all largely nothing more than Common Sense, of course .. except for the constant and consistent gross assumption that "Courts" and "the Judiciary" have 'power' over the situation (i.e. as if they could make any Law). Law only comes from sworn Statements of Truth and Juries ... not Judges of any kind, high or low.
("Law", coming from a Judge, is indistinguishable from "tyranny" ... unless it completely matches Common Sense ... which everything below actually does ... in which case ... since it's nothing more than Common Sense ... why did it need a Judge to say it? We all have as much Common Sense as anyone else).
It is, therefore, only the Common Sense expressed below, that has any LAWFUL validity, and "deference + forelock-tugging to Courts/Judiciaries" is nothing more than "legal bollox".
Pritchard (deceased)  Upjohn LJ confirmed that:
(i) a fundamental defect in proceedings will make the whole proceedings a nullity;
(ii) a nullity cannot be waived;
(iii) it is never too late to raise the issue of nullity; and
(iv) a person affected by a void order has the right – ex debito justitiae ("as of Right" ... i.e. a litigant is entitled to it merely upon the asking for it - as opposed to something which may be a matter of judicial discretion or determination.) – to have it set aside.
A 'voidable' Order is one that could be voided if brought to the attention of a Higher Court.
1978: Although a void order has no legal effect from the outset, it may sometimes be necessary to have it set aside because as Lord Radcliffe once said: “It bears no brand of invalidity on its forehead”.
In Bellinger v Bellinger  the House of Lords confirmed that:
(i) a void act is void from the outset; and
(ii) no Court – not even the House of Lords (now the Supreme Court) has jurisdiction to give legal effect to a void act no matter how unreasonable that may seem because doing so would mean reforming the laws which no Court has power to do because such power rests only with Parliament. The duty of the Court is to interpret and apply the law not reform it(*).
[* Not true, of course: Only a Jury (in a Court de jure), or sworn Statements of Truth, have the power to make Law. No? OK ... then what's the point of a Jury, then?]
A ‘void’ order or claim has no legal effect ab initio (from the beginning/outset) and therefore does not need to be appealed, although for convenience it may sometimes be necessary to have it set aside (Lord Denning in MacFoy v United Africa Co. Ltd.  and Firman v Ellis ), whereas a ‘voidable’ order or claim has legal effect unless and until it is set aside.
Therefore, while a void order or claim does not have to be obeyed, and can be ignored and its nullity can be relied on as a defence when necessary (Wandsworth London Borough Council v. Winder  A.C. 461), a voidable order or claim has to be obeyed and cannot be ignored unless and until it is set aside.
A ‘void’ order can be set aside by the Court which made the order, because the Court has inherent jurisdiction to set aside its own void order (Lord Greene in Craig v Kanssen ), whereas a ‘voidable’ order can only be set aside by appeal to an appellate Court.
A void order is incurably void, and all proceedings based on the invalid claim or void act are also void. Even a decision of the higher Courts (High Court, Court of Appeal and Supreme Court) will be void if the decision is founded on an invalid claim or void act, because something cannot be founded on nothing (Lord Denning in MacFoy v United Africa Co. Ltd. ).
It is never too late to raise the issue of nullity, and a person can ignore the void order or claim and raise it as a defence when necessary (Wandsworth London Borough Council v. Winder  A.C. 461; Smurthwaite v Hannay  A.C. 494; Upjohn LJ in Re Pritchard (deceased) ; Lord Denning in MacFoy v United Africa Co. Ltd. ).
Some of the case precedents relating to Void Orders:-
Crane v Director of Public Prosecutions : If an order is void ab initio (from the beginning) then there is no real order of the Court.
In MacFoy v United Africa Co Ltd.  Lord Denning confirmed that:
(i) a void order is automatically void without more ado;
(ii) a void order does not have to be set aside by a Court to render it void - although for convenience it may sometimes be necessary to have the Court set the void order aside;
(iii) a void order is incurably void and all proceedings based on the void order/invalid claim are also void.
A Solicitor enlarges the detail
Veronica, June 2012