is it possible to convert directly from for example Spanish F Atpl to UK ATPL provided that all the requirements of hours and checking are met?
Not possible
AFAIK. Under JAR the only thing you can do is change the State of licence issue, the licence itself cannot change in the process. You need to convert your Spanish CPL to a UK/JAR CPL before you can upgrade to a UK/JAR ATPL.
If you meet the hours requirement for an ATPL your best bet might be to get your Spanish ATPL issued first, which should remove the 'copilot only' limitation, before converting that to a UK/JAR ATPL.
You are going to pay twice regardless (upgrade-transfer or transfer-upgrade) so from that point of view it makes no difference.
(all this based on theory only, I have no experience dealing with the Spanish aviation authorities)