Zeph still barking!! Bless him

Hi There

Here are a few more details about the barking habits of Zeph

1: What time does the barking start?

Last night he was put to bed about 11.45 pm after a late 15 minute walk in the park, barking started at about 12.15 am and finished at 6.45 am when we got up!
We tried to ignore it as much as possible I got up once but did not enter the room as I have done on previous nights I just rapped on the door loudly as I have read this can stop them, it did for 3 minutes but then he started again.

2: Could it be badgers/foxes that are disturbing him?

I don't think this is the case.

3: Could it be any neighbours moving about?

No they get up at the same time as us, we have been around to tell them that we are having a problem with Zeph at the moment and they seem to be OK with it.

4: Could it be your central heating switching on/off?

The central heating comes on at 7 am so it can't be that.

The only thing that comes to mind is that he was unwell last Wednesday/Thursday with the runs we got up to let him out to relieve himself, but this is sorted now after a visit to the vets last Friday

I have tried the following:

Radio on low, item of clothing in his crate, toys, late night walk.

The having him in the bedroom is not an option for us.

As I type this he is fast asleep at my feet!!!