Passport expires in 5,5 months

***

I would be very suspicious of anyone stating here on the forum that they can help with passports or visas.
New passports have to be issued by the relevant embassy. Visa extensions are not issued for passports with less than 6 months validity.

There use to be a passport extension option available  but I think that was scrapped a few years ago.
Your only serious chance is to contact the embassy in Jakarta on the off chance it can be done.

If your having VOA,there are some immigration offices require a domisili extending your visa

If your in visa 211 (tourist visa as well
It require your sponsor letter and a domisili letter as well.

If your passport is expiring 5.5month I do not see any problem unless they give you a hard time.

cheers,
rick

A free VOA can't be extended (worth a mention).
If the OP has an extendable visa, immigration should require six months validity, but you never know your luck so it won't hurt to try.

It’s up to immigration to extend a visa with less than 6 months on the passport so this does vary from place to place, also check with your connection country for travelling back again airlines and as an example only Singapore could refuse you entry unless in transit (Landing and not leaving the airport)
I would certainly be in contact with the embassy like yesterday no one on here can give you a yes no answer only uk government officials can
If you already have your return ticket issued thats great, booking one may be difficult then again may not, try and get a direct flight to the uk in this case
Your wasting your time and money using any agents for renewal or extensions it will be an expensive scam 100% so ignore any agent even for extending a visa you’ll dig yourself a huge hole
I would advise in the future to get a 2nd passport when staying in any country for extended periods all uk citizens are eligible I have 3 but this is difficult and for certain countries I travel to with certain visas ie Russia / Ukraine etc