I would expect their reluctance to have something to do with cost of employing at your prior seniority level relative to those newbies (if they were allowed to do so), combined with breach of the union-agreed seniority rules on a "new hire", even though you would admittedly be a rehire. I would imagine that if you applied and had enough time to re-retirement age remaining to economically justify training however, you would be at the front of any pool, whatever "HR" tell you prior to actual job offer.
Furthermore, since you no longer have a contract, you would open BA to litigation to employ you ahead of another suitably experienced pilot, as you have not been in a "furlogh" scheme - such as our US friends use on occassion.