  For tenderers established in the United Kingdom:  Please be aware that after the UK's withdrawal from the EU, the rules of access to EU  procurement procedures of economic operators established in third countries will apply to  tenderers from the UK depending on the terms of any Withdrawal Agreement. In case such  access is not provided by legal provisions in force tenderers from the UK could be rejected from  the procurement procedure.  Any economic operator willing to submit a tender for this call for tenders must be registered in  the Participant Register - an online register of organisations and natural persons participating in  European Commission's calls for tenders or proposals (participants). On registering each participant obtains a Participant Identification Code (PIC, 9-digit number)  which acts as its unique identifier in the Participant Register. A participant needs to register only  once – the information provided can be further updated or re-used by the participant in other  European Commission's calls for tenders or calls for proposals. At any moment during the procurement procedure the Research Executive Agency Validation  Services (hereafter  the EU Validation Services) may contact the participant and ask for  supporting documents on legal existence and status. The requests will be made through the  register's messaging system to the e-mail address of the participant's contact person indicated in  the register. It is the responsibility of the participant to provide a valid e-mail address and to  check it regularly.  The documents that may be requested by  the EU Validation Services  are listed in the EU Grants  and Tenders Rules on Legal Entity Validation, LEAR appointment and Financial Capacity  assessment.   Please note that a request for supporting documents by the  EU Validation Services  in no  way implies that the tenderer has been successful.  Economic operators can submit a tender either as a sole tenderer or as a group of tenderers. In  either case subcontracting is permitted. In order to fulfil the selection criteria set out in  Section 3.2 the tenderer can rely on the  capacities of subcontractors or other entities (not subcontractors).  The role of each entity involved in a tender (hereafter referred to as  involved entity ) must be  clearly specified: sole tenderer, member of a group or Group leader, subcontractor or an entity on  18 2.4 Ways to submit a tender: how can economic operators organise themselves to  submit a tender?  2.3 Registration in the Participant Register: why register? 