| 
he | 
 is | 
less likely [ than Ivy
  ] | 
[[ to have spoken ]] | 
| 
Sub- | 
Finite | 
Complement | 
-ject | 
| 
Mo- | 
Residue | 
-od | |
cf he having spoken is less likely than Ivy (having done so).
| 
he | 
 is | 
less likely than Ivy | 
to | 
have | 
spoken | 
| 
Subject | 
Operator/Auxiliary | 
Auxiliary Extension | 
Infinitive  | 
Auxiliary | 
Main Verb | 
That is, Fawcett analyses 'spoken' as the Main Verb of this attributive clause, and 'is' and 'have' as two of its Auxiliaries.
 
