Merging of loan parts

Nope - you're stuck with them all unfortunately

That's a shame.  It means, if I understand correctly, that there's no point buying up loans with less than 50p balance, as you'd never get a whole penny interest.  And it would make lenders' and Lendy's maintenance overhead significantly reduced.  

Like sam i am I haven't bought a loan this small (you haven't come over from Assetz have you?) but the issue that concerns you does not just apply to loan parts under 50p, it could apply to a loan of any size.  Consider a loan of £98.12 - if you held for the full 31 days of July you would get exactly £1.00 interest. However you might think there is no point loaning for instance an extra 42p - £98.54 because you would still get the same £1.00 interest for the month.  However by the end of September the £98.12 amount will have paid £2.97 for 92 days interest whereas a principal of £98.54 will have paid £2.98 interest.  In other words interest is calculated on a cumulative basis using the number of days since the loan part start date. And that is the reason I guess why you cannot merge different loan parts for the same loan because they will have different start dates.

If the problem gets too bad, you can amalgamate your parts buy selling several parts on the secondary market then buying them back as one lump.  This is very hazardous but I have done it successfully many times (and got caught by the hazards a few times).
1) Choose a time when there is nothing for sale for the loan in question.
2) Ensure the secondary market is not jammed up by an earlier overdrawn transaction.  I test this by selling £1 of the loan and buying it straight back.  If my sale goes through then I know the secondary market is not jammed up.
3) Sell all the loan parts you want to amalgamate.
4) Immediately buy back the whole amount in one transaction.  You have bought back your own loan parts but they are now amalgamated into a single part.
5) You need enough spare cash to buy back the whole amalgamated loan part.  I have never been brave enough to do this operation without the cash in my account, but in theory you could create a BACS deficit for the necessary cash at the start then offset the BACS deficit when the cash is released back at the end of the process.
6) You risk losing your precious loan parts if someone else manages to buy them back before you do.  Be as quick as you can and choose a quiet time.
7) I clearly have too much time on my hands.

I would not use this system whilst there is a suspicion that bots are at work. You can't be faster than a bot and could lose the lot.

absolutely, my point is that with minimal basic spreadsheet work (some people view pivot tables as 'advanced) pulling this information together takes little effort.