Chris (buenchico) is right to be wary of the pro rata bit - it could be pro rata to a 35, 37.5 or even 40 hour week!!
(Hi Chris, by the way - long time no post!)
However, the 30 hour week may suit your needs, even if it pays "less" - only you know your reasons for wanting to return to work!
The other thing about public sector pay scales is the ability / opportunity to progress.
Both jobs offer a salary range, so you could expect to enter at the lower end and progress to the higher.
However, with one position, you may receive an increase after completion of, say, six months, and then incremental increases after that, but never be able to progress beyond that Grade / Scale / Band.
The other, you may have opportunities to progress to a higher Grade / Scale / Band with greater earning potential more quickly, even though the starting salary is less.
You need to find out how the pay structure works for each position, - ask at any interview if necessary - and whether the the position is Scale-restricted or 'capped'. This means you could work in the same job for 55 years and not be allowed to progress to the next scale irrespective of your ability!!
The second of your jobs looks like it is capped, ("bar at �20,736") ?? Which means it may not be the best long-term career move even though it pays better initially.
I used to work in Local Authority Education, and our Borough's pay scales were totally different to the neighbouring Borough's - not in terms of salary, but structure - if we used Scale F's, G's and H's the other Borough's would use Grade 1's, 2's and 3's!!
All I can advise is find out as much as you can and pick the one that most suits you and your situation !
Wishing you all the best for next week!
pod x