Assuming you are an EASA licence holder:
Part FCL 625(C).
FCL.625.A IR(A) — Revalidation
(a) Revalidation. Applicants for the revalidation of an IR(A):
(1) when combined with the revalidation of a class or type rating, shall pass a proficiency check
in accordance with Appendix 9 to this Part;
(2) when not combined with the revalidation of a class or type rating, shall:
(i) for single-pilot aeroplanes, complete section 3b and those parts of section 1
relevant to the intended flight, of the proficiency check prescribed in Appendix 9 to
this Part; and
(ii) for multi-engine aeroplanes, complete section 6 of the proficiency check for single-
pilot aeroplanes in accordance with Appendix 9 to this Part by sole reference to
instruments.
(3) An FNPT II or an FFS representing the relevant class or type of aeroplane may be used in
the case of paragraph (2), but at least each alternate proficiency check for the revalidation of
an IR(A) in these circumstances shall be performed in an aeroplane.
(b) Cross-credit shall be given in accordance with Appendix 8 to this Part.
Bottom line, speak to your new employer. Depending on your experience levels and ops department policy, you MAY be able to start with a lapsed IR. You will be getting one as part of your Type ratings anyhow I expect, some will be flexible to this. Others will insist you have an in date IR. Explain the situation to them, tell them you have no problem renewing, but ask if it's essential to start your training. Will save you a few Bob if you get a positive response.