The UK now removes EU citizens and family members before their deportation appeal takes place. Obviously, this interferes with the life that the person has established in the UK (job and home may be lost, for example), in effect prejudges the outcome of the appeal, has a drastic impact on family members and also interferes somewhat with preparing the appeal.
However, it is possible for such an individual to re-enter the UK for the purpose of attending the appeal hearing, for example to give evidence. In R (on the application of Gabor) v Secretary of State for the Home Department (Reg 29AA: interpretation)  UKUT 00287 (IAC) the Upper Tribunal addresses the test for readmission and the procedure.
The official headnote:
1. An application for Temporary Admission pursuant to reg 29AA of the Immigration (EEA) Regulations 2006 must be granted unless the applicant’s appearance may cause serious troubles to public policy or public security. Proportionality is not the test, and the cost of facilitating the applicant’s appearance is not a relevant consideration. The test is whether it can be said properly that there is the necessary basis for refusing leave pursuant to para 29AA(3).
2. “Appearance”, in this context, means presence in the UK for the purpose of attending the hearing (Kasicky doubted).
3. Where admission is granted for this purpose it must take place within a reasonable time to allow the applicant properly to instruct his solicitors. Normally, some 2 or 3 days before the hearing will be required.
The detail of the judge’s consideration of the timing of re-entry is worth quoting in full:
To be allowed to enter to appear seems to me to mean that it must be right that the admission takes place within a reasonable time to enable the applicant properly to instruct his solicitors. True it is of course that when the applicant is abroad one would expect that he is able to make some submissions but in any case it is necessary for solicitors to take proper instructions, maybe to find witnesses who could assist him in the given case and it seems to me that the requirement to give leave to enter to appear carries with it that the applicant should be enabled to make appearance which is one which is based on proper advice and proper instructions to those representing him. This does not mean that there need be a lengthy period before the hearing. Quite the contrary: I note that the solicitors asked for a matter of weeks; that is not reasonable but it does seem to me that normally some two possibly three days before the hearing date is required. In this case the hearing date is fixed for 8 November which happens to be a Tuesday and one has to bear in mind the intervening weekend. In those circumstances what I propose to direct is that the admission be permitted to take place on the Thursday, that is Thursday 3 November. He will then no doubt be taken to immigration detention which should be Harmondsworth and the solicitors should then visit him for the purpose of taking instructions on Friday, the 4th and the Home Office must ensure that access on the 4th is allowed even if that does mean perhaps jumping the queue because one knows that there are pressures on attending at the immigration centres for legal visits.
Source: R (on the application of Gabor) v Secretary of State for the Home Department (Reg 29AA: interpretation)  UKUT 00287 (IAC)