That is not true, he avoided that term. He believed that demons could have an influence on the human body but not demon possession. So that is not the case, he never once said a person could be demon possessed. He has given accounts of why he does not use the term demon possession.

He has a brilliant way of explaining his teachings, keeping them simplified.

Possession means having total control over something, owning it, Derek Prince did not believe that. He believed in demon influence over someone.

How could something so biblical be a dangerous false doctrine?

Luke 10:19 New International Version (NIV)
19 I have given you authority to trample on snakes and scorpions and to overcome all the power of the enemy; nothing will harm you.

Matthew 17:19-20 King James Version (KJV)
19 Then came the disciples to Jesus apart, and said, Why could not we cast him out?

20 And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.

Ephesians 1:20-21 King James Version (KJV)
20 Which he wrought in Christ, when he raised him from the dead, and set him at his own right hand in the heavenly places,

21 Far above all principality, and power, and might, and dominion, and every name that is named, not only in this world, but also in that which is to come:

Mark 16:17 King James Version (KJV)
17 And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues;

Matthew 10:8 King James Version (KJV)
8 Heal the sick, cleanse the lepers, raise the dead, cast out devils: freely ye have received, freely give.

Oh, here I just found a whole bunch. Hallelujah, I don't have to hunt them all up!

Matthew 10:8
Verse Concepts
"Heal the sick, raise the dead, cleanse the lepers, cast out demons. Freely you received, freely give.

Matthew 10:1
Verse Concepts
Jesus summoned His twelve disciples and gave them authority over unclean spirits, to cast them out, and to heal every kind of disease and every kind of sickness.

Mark 3:15
Verse Concepts
and to have authority to cast out the demons.

Mark 16:17
Verse Concepts
"These signs will accompany those who have believed: in My name they will cast out demons, they will speak with new tongues;

Mark 6:13
Verse Concepts
And they were casting out many demons and were anointing with oil many sick people and healing them.

Acts 8:7
Verse Concepts
For in the case of many who had unclean spirits, they were coming out of them shouting with a loud voice; and many who had been paralyzed and lame were healed.

Acts 16:18
Verse Concepts
She continued doing this for many days. But Paul was greatly annoyed, and turned and said to the spirit, "I command you in the name of Jesus Christ to come out of her!" And it came out at that very moment.

Acts 19:12
Verse Concepts
so that handkerchiefs or aprons were even carried from his body to the sick, and the diseases left them and the evil spirits went out.

Matthew 7:22
Verse Concepts
"Many will say to Me on that day, 'Lord, Lord, did we not prophesy in Your name, and in Your name cast out demons, and in Your name perform many miracles?'

Mark 9:38
Verse Concepts
John said to Him, "Teacher, we saw someone casting out demons in Your name, and we tried to prevent him because he was not following us."

Luke 9:49
Verse Concepts
John answered and said, "Master, we saw someone casting out demons in Your name; and we tried to prevent him because he does not follow along with us."

Acts 19:13
Verse Concepts
But also some of the Jewish exorcists, who went from place to place, attempted to name over those who had the evil spirits the name of the Lord Jesus, saying, "I adjure you by Jesus whom Paul preaches."

Matthew 12:27
Verse Concepts
"If I by Beelzebul cast out demons, by whom do your sons cast them out? For this reason they will be your judges.

Luke 11:19
Verse Concepts
"And if I by Beelzebul cast out demons, by whom do your sons cast them out? So they will be your judges.

Mark 9:18
Verse Concepts
and whenever it seizes him, it slams him to the ground and he foams at the mouth, and grinds his teeth and stiffens out. I told Your disciples to cast it out, and they could not do it."

Luke 9:40
Verse Concepts
"I begged Your disciples to cast it out, and they could not."

Matthew 17:19
Verse Concepts
Then the disciples came to Jesus privately and said, "Why could we not drive it out?"

Mark 9:28
Verse Concepts
When He came into the house, His disciples began questioning Him privately, "Why could we not drive it out?"

https://bible.knowing-jesus.com/topics/People-Casting-Out-Demons